Develop Reference

Checking With Assertion

The methods setDates and setTimes have as preconditions that none of their arguments are null. This is to be checked by means of an assertion. (This means that if the precondition is not met, the program will fail at the assertion, and an AssertionError will be thrown.)
here is my code:
public class Section
{
/**
* Default section number.
*/
private static final String DEFAULT_SECTION_NUMBER = "";
/**
* Constant for building Strings with newline characters within them.
*/
private static final String LINE_SEPARATOR = System.
getProperty("line.separator");
/**
* The maximum number of students permitted into a section.
*/
private static final int MAXIMUM_STUDENTS_PER_SECTION = 30;
/**
* Valid length for a sectionNumber string.
*/
private static final int SECTION_NUMBER_LENGTH = 3;
/**
* Shared variable for keeping count of the number of section objects in
* existence.
*/
private static int count = 0;
/**
* The date at which the section is finished.
*/
private Date endDate;
/**
* The end time for the meeting of the section.
*/
private Time2 endTime;
/**
* The list of students in the class. This declaration uses the Java 7 facility
* of not repeating the generic type if that type can be inferred by the
* compiler.
*/
private final List<Student> roster = new ArrayList<>();
/**
* The three-character designation of the section (called a
* “number”).
*/
private String sectionNumber = DEFAULT_SECTION_NUMBER;
/**
* The date on which the section starts to meet.
*/
private Date startDate;
/**
* The time of day at which the section meets.
*/
private Time2 startTime;
/**
* The course of which this is a section.
*/
private final Course thisCourse;
/**
* Constructor.
*
* #param course the course of which this is a section
* #param sectionNumber the section number (within the course) of this section
* #throws SectionException
*/
public Section(Course course, String sectionNumber) throws SectionException
{
/* Increment the collective count of all Section objects that have been
created. Do this first as the object already exists. */
++count;
this.thisCourse = course;
try
{
if( isValidSectionNumber(sectionNumber) )
this.sectionNumber = sectionNumber;
}
catch (Exception ex)
{
throw new SectionException("Error in constructor", ex);
}
}
/**
* Add a student to the course.
*
* #param student the student object to be added. If the course is full, the
* student is not added
*/
public void addStudent(Student student)
{
if( roster.size() != MAXIMUM_STUDENTS_PER_SECTION )
roster.add(student);
}
/**
* Get details about the current state of this section, including the course of
* which it is part, the dates it starts and ends, times, etc., and the current
* count of the enrollment.
*
* #return the section details
*/
public String getDetails()
{
return String.join(LINE_SEPARATOR,
"Section: " + this.toString(),
"Course: " + thisCourse.getDetails(),
"Dates: " + startDate + " to " + endDate,
"Times: " + startTime + " to " + endTime,
"Enrollment: " + roster.size());
}
/**
* Create a string that represents the information about the students in the
* course.
*
* #return a string that represents the information about the students in the
* course
*/
public String getRoster()
{
/* The following commented-out code is the obvious way to do this, using
String concatenation (and this is acceptable). However, the recommended
Java approach to this kind of operation is to use a StringJoiner (new
class in Java 8), as this uses less garbage collection resources. */
// String result = "";
// for( Student student : roster )
// {
// result += ( result.isEmpty() ? "" : LINE_SEPARATOR) + student;
// }
// return result;
StringJoiner stringJoiner = new StringJoiner(LINE_SEPARATOR);
for( Student student : roster )
stringJoiner.add(student.toString());
return stringJoiner.toString();
}
/**
* Get a count of the number of students registered (on the roster) for this course.
*
* #return a count of the number of students registered for this course
*/
public int getRosterCount()
{
return roster.size();
}
/**
* Get the section number for this course.
*
* #return the section number for this course
*/
public String getSectionNumber()
{
return sectionNumber;
}
/**
* Set the start and end dates for the section.
*
* #param startDate the start date
* #param endDate the end date
*/
public void setDates(Date startDate, Date endDate)
{
/* There is no requirement to validate these. */
this.startDate = startDate;
this.endDate = endDate;
}
/**
* Set the start time and the end time for the meetings of the section.
*
* #param startTime the start time for meetings of the section
* #param endTime the end time for the meetings of the section
*/
public void setTimes(Time2 startTime, Time2 endTime)
{
/* There is no requirement to validate these. */
this.startTime = startTime;
this.endTime = endTime;
}
/**
* Section number (prefixed)
*
* #return Section number (prefixed)
*/
#Override
public String toString()
{
return thisCourse.toString() + "-" + sectionNumber;
}
/**
* Finalization. Reduce the instance count by 1.
*
* #throws Throwable standard interface.
*/
#SuppressWarnings("FinalizeDeclaration")
#Override
protected void finalize() throws Throwable
{
/* Decrement the count of the collective total of all Section objects. */
--count;
super.finalize();
}
/**
* Get a count of how many total Section objects are currently in existence.
*
* #return a count of how many Section objects are currently in existence
*/
public static int getSectionCount()
{
return count;
}
/**
* Validate the sectionNumber string. It must be of the correct length.
*
* #param sectionNumber the sectionNumber string
* #return true if the string if valid, otherwise false
*/
private static boolean isValidSectionNumber(String sectionNumber)
{
return sectionNumber != null &&
sectionNumber.length() == SECTION_NUMBER_LENGTH;
}
}
would i simply place 'assert' before this.startDate = startDate; and so forth??? my book only has one example and it is for ensuring a value is between 0 and 10.
this is the example my book uses:
public class AssertTest
{
public static void main(string[] args)
{
Scanner input = new Scanner(System.in);
System.out.print("Enter a number between 0 and 10: ");
int number = input.nextInt();
//assert that the value is >= 0 and <= 10
assert (number >= 0 && number <= 10) : "bad number: " + number;
System.out.printf("You entered %d%n", number);
}
}
so could i say
assert this.startDate = startDate
assert this.endDate = endDate
and so on?

First of all the methods setTime and setDates are public what suggests that they may be used outside of the package. Given that you have no control over parameters - using assert would not be considered as the best practice. You should rather use Runtime Exceptions such as IllegalArgumentException when value can be supplied externally (and you have no control over it):
if (startDate == null || endDate == null)
throw new IllegalArgumentException("Non-null arguments are required");
The syntax for the Assert would be as follows:
assert startDate != null;
assert endDate != null;
You can also use the following syntax in order to output additional information when assertion fails:
assert startDate != null : "startDate was set to null"
assert endDate != null : "endDate was set to null"

Why is my object staying null?

For some reason, I can't seem to fix this giving me a NullPointerException. I print out poly.term.degree without any errors, and then set poly.next equal to poly and then get a nullPointerException when I try to print out poly.next.term.degree which should seemingly be the same. I'm aware this is incomplete code but I think this is my main issue.
public Polynomial add(Polynomial p)
{
Polynomial newPoly = new Polynomial();
newPoly.poly = new Node(0,0,null);
Polynomial myCurr = this;
Polynomial otherCurr = p;
while(myCurr.poly != null)
{
int myDeg = myCurr.poly.term.degree;
int otherDeg = p.poly.term.degree;
float myCo = myCurr.poly.term.coeff;
float otherCo = otherCurr.poly.term.coeff;
if(myDeg == otherDeg)
{
System.out.println("degrees "+myDeg + " and "+ otherDeg+ " are equal, creating new node...");
Node n = new Node(myCo+otherCo,p.poly.term.degree, newPoly.poly.next);
System.out.println(newPoly.poly.term.degree);
newPoly.poly.next = newPoly.poly;
newPoly.poly = n;
System.out.println(newPoly.poly.next.term.degree); // Gives me a NullPointerException
}
Also, the constructors and everything for these classes is below.
package poly;
import java.io.*;
import java.util.StringTokenizer;
/**
* This class implements a term of a polynomial.
*
* #author runb-cs112
*
*/
class Term {
/**
* Coefficient of term.
*/
public float coeff;
/**
* Degree of term.
*/
public int degree;
/**
* Initializes an instance with given coefficient and degree.
*
* #param coeff Coefficient
* #param degree Degree
*/
public Term(float coeff, int degree) {
this.coeff = coeff;
this.degree = degree;
}
/* (non-Javadoc)
* #see java.lang.Object#equals(java.lang.Object)
*/
public boolean equals(Object other) {
return other != null &&
other instanceof Term &&
coeff == ((Term)other).coeff &&
degree == ((Term)other).degree;
}
/* (non-Javadoc)
* #see java.lang.Object#toString()
*/
public String toString() {
if (degree == 0) {
return coeff + "";
} else if (degree == 1) {
return coeff + "x";
} else {
return coeff + "x^" + degree;
}
}
}
/**
* This class implements a linked list node that contains a Term instance.
*
* #author runb-cs112
*
*/
class Node {
/**
* Term instance.
*/
Term term;
/**
* Next node in linked list.
*/
Node next;
/**
* Initializes this node with a term with given coefficient and degree,
* pointing to the given next node.
*
* #param coeff Coefficient of term
* #param degree Degree of term
* #param next Next node
*/
public Node(float coeff, int degree, Node next) {
term = new Term(coeff, degree);
this.next = next;
}
}
/**
* This class implements a polynomial.
*
* #author runb-cs112
*
*/
public class Polynomial {
/**
* Pointer to the front of the linked list that stores the polynomial.
*/
Node poly;
/**
* Initializes this polynomial to empty, i.e. there are no terms.
*
*/
public Polynomial() {
poly = null;
}
/**
* Reads a polynomial from an input stream (file or keyboard). The storage format
* of the polynomial is:
* <pre>
* <coeff> <degree>
* <coeff> <degree>
* ...
* <coeff> <degree>
* </pre>
* with the guarantee that degrees will be in descending order. For example:
* <pre>
* 4 5
* -2 3
* 2 1
* 3 0
* </pre>
* which represents the polynomial:
* <pre>
* 4*x^5 - 2*x^3 + 2*x + 3
* </pre>
*
* #param br BufferedReader from which a polynomial is to be read
* #throws IOException If there is any input error in reading the polynomial
*/
public Polynomial(BufferedReader br) throws IOException {
String line;
StringTokenizer tokenizer;
float coeff;
int degree;
poly = null;
while ((line = br.readLine()) != null) {
tokenizer = new StringTokenizer(line);
coeff = Float.parseFloat(tokenizer.nextToken());
degree = Integer.parseInt(tokenizer.nextToken());
poly = new Node(coeff, degree, poly);
}
}

I think the problem lies here:
newPoly.poly.next = newPoly.poly;
newPoly.poly = n;
At first you say, that newPoly.poly.next = newPoly.poly; so you assign the current element to the next, which is recursive. And then you say newPoly.poly = n; . So you assign a new element to newPoly. I think that the garbage collector deletes the newPoly element, because it is overwritten, so you lose the reference to the newPoly element. Which means when you access it later you get a nullpointer exception. You could fix this like this:
newPoly.poly.next = n;
//and dont forget to set the next pointer of the new elemnt to 0
n.next = NULL;
Just assign the new element to the next element.
EDIT
#hendersawn
You could sort the list. See below:
sort(Node head_p){ //do not change the head, or you will lose the beginning.
Node tmp_p;
Node curr_p = head_p;
while(curr_p != NULL){
if(curr_p.poly.term.degree < curr_p.next.poly.term.degree) //either degree is smaller or greater
{//swap
tmp_p = curr_p; //save first element
curr_p = curr_p.next; //set first element to second
//now the 2 element is the actual third element so we need
//to put the first between the second and the third
tmp_p.next = curr_p.next; //set next of first to third
curr_p.next = tmp_p; //set second element to the first that we saved before
}
curr_p = curr_p.next; //move to next element...rinse repeat
}
}

newPoly might be null
newPoly.poly might be null
newPoly.poly.next might be null
newPoly.poly.next.term might be null
or
newPoly.poly.next.term.degree might be null.
To avoid NullPointerException, you need to make sure that any member used is initialized with a proper value.

Nothing is obviously null that I can tell, however with four 'dots' (something.something.something.something) of Object Oriented Indirection, you're going to encounter this problem a lot. Usually two - three 'dots' on a single line are all you should ever do, but since that's more about the design and not the error, I digress.
The way to find this problem would be to either:
Put a breakpoint right at that line and see what the variables are there, and which one is null or
Do a System.out.println for each of the components to see which one breaks it, and work backwards from there. ex:
System.out.println(newPoly.poly.next.term.degree); // Gives me a NullPointerException
System.out.println(newPoly);
System.out.println(newPoly.poly);
System.out.println(newPoly.poly.next);
System.out.println(newPoly.poly.next.term);
because the nullPointerException would only get thrown on one of those (it can't be degree, otherwise that statement would have just printed 'null'
if I had to bet, I'd say it's probably newPoly.poly.next which is null
the lines:
newPoly.poly.next = newPoly.poly;
newPoly.poly = n;
Superficially seem like they would be the culprit of your trouble, since you're assigning the 'next' of your newPoly.poly, but then you re-assign your newPoly.poly, and lose that old reference to .next, I think.
Good luck! hope that helps.

Print the data in ResultSet along with column names

I am retrieving columns names from a SQL database through Java. I know I can retrieve columns names from ResultSet too. So I have this sql query
select column_name from information_schema.columns where table_name='suppliers'
The problem is I don't know how can I get columns names from ResultSet and my code is
public void getAllColumnNames() throws Exception{
String sql = "SELECT column_name from information_schema.columns where table_name='suppliers'";
PreparedStatement ps = connection.prepareStatement(sql);
ResultSet rs = ps.executeQuery(sql);
// extract values from rs
}

ResultSet resultSet = statement.executeQuery("SELECT * from foo");
ResultSetMetaData rsmd = resultSet.getMetaData();
int columnsNumber = rsmd.getColumnCount();
while (resultSet.next()) {
for (int i = 1; i <= columnsNumber; i++) {
if (i > 1) System.out.print(", ");
String columnValue = resultSet.getString(i);
System.out.print(columnValue + " " + rsmd.getColumnName(i));
}
System.out.println("");
}
Reference : Printing the result of ResultSet

1) Instead of PreparedStatement use Statement
2) After executing query in ResultSet, extract values with the help of rs.getString() as :
Statement st=cn.createStatement();
ResultSet rs=st.executeQuery(sql);
while(rs.next())
{
rs.getString(1); //or rs.getString("column name");
}

use further as
rs.getString(1);
rs.getInt(2);
1, 2 is the column number of table and set int or string as per data-type of coloumn

For those who wanted more better version of the resultset printing as util class
This was really helpful for printing resultset and does many things from a single util... thanks to Hami Torun!
In this class printResultSet uses ResultSetMetaData in a generic way have a look at it..
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.StringJoiner;
public final class DBTablePrinter {
/**
* Column type category for CHAR, VARCHAR
* and similar text columns.
*/
public static final int CATEGORY_STRING = 1;
/**
* Column type category for TINYINT, SMALLINT,
* INT and BIGINT columns.
*/
public static final int CATEGORY_INTEGER = 2;
/**
* Column type category for REAL, DOUBLE,
* and DECIMAL columns.
*/
public static final int CATEGORY_DOUBLE = 3;
/**
* Column type category for date and time related columns like
* DATE, TIME, TIMESTAMP etc.
*/
public static final int CATEGORY_DATETIME = 4;
/**
* Column type category for BOOLEAN columns.
*/
public static final int CATEGORY_BOOLEAN = 5;
/**
* Column type category for types for which the type name
* will be printed instead of the content, like BLOB,
* BINARY, ARRAY etc.
*/
public static final int CATEGORY_OTHER = 0;
/**
* Default maximum number of rows to query and print.
*/
private static final int DEFAULT_MAX_ROWS = 10;
/**
* Default maximum width for text columns
* (like a VARCHAR) column.
*/
private static final int DEFAULT_MAX_TEXT_COL_WIDTH = 150;
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* {#link #DEFAULT_MAX_ROWS} and
* {#link #DEFAULT_MAX_TEXT_COL_WIDTH} will be used to limit
* the width of text columns (like a VARCHAR column).
*
* #param conn Database connection object (java.sql.Connection)
* #param tableName Name of the database table
*/
public static void printTable(Connection conn, String tableName) {
printTable(conn, tableName, DEFAULT_MAX_ROWS, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* maxRows and
* {#link #DEFAULT_MAX_TEXT_COL_WIDTH} will be used to limit
* the width of text columns (like a VARCHAR column).
*
* #param conn Database connection object (java.sql.Connection)
* #param tableName Name of the database table
* #param maxRows Number of max. rows to query and print
*/
public static void printTable(Connection conn, String tableName, int maxRows) {
printTable(conn, tableName, maxRows, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* maxRows and
* maxStringColWidth will be used to limit
* the width of text columns (like a VARCHAR column).
*
* #param conn Database connection object (java.sql.Connection)
* #param tableName Name of the database table
* #param maxRows Number of max. rows to query and print
* #param maxStringColWidth Max. width of text columns
*/
public static void printTable(Connection conn, String tableName, int maxRows, int maxStringColWidth) {
if (conn == null) {
System.err.println("DBTablePrinter Error: No connection to database (Connection is null)!");
return;
}
if (tableName == null) {
System.err.println("DBTablePrinter Error: No table name (tableName is null)!");
return;
}
if (tableName.length() == 0) {
System.err.println("DBTablePrinter Error: Empty table name!");
return;
}
if (maxRows
* ResultSet to standard out using {#link #DEFAULT_MAX_TEXT_COL_WIDTH}
* to limit the width of text columns.
*
* #param rs The ResultSet to print
*/
public static void printResultSet(ResultSet rs) {
printResultSet(rs, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method to print rows of a
* ResultSet to standard out using maxStringColWidth
* to limit the width of text columns.
*
* #param rs The ResultSet to print
* #param maxStringColWidth Max. width of text columns
*/
public static void printResultSet(ResultSet rs, int maxStringColWidth) {
try {
if (rs == null) {
System.err.println("DBTablePrinter Error: Result set is null!");
return;
}
if (rs.isClosed()) {
System.err.println("DBTablePrinter Error: Result Set is closed!");
return;
}
if (maxStringColWidth columns = new ArrayList(columnCount);
// List of table names. Can be more than one if it is a joined
// table query
List tableNames = new ArrayList(columnCount);
// Get the columns and their meta data.
// NOTE: columnIndex for rsmd.getXXX methods STARTS AT 1 NOT 0
for (int i = 1; i maxStringColWidth) {
value = value.substring(0, maxStringColWidth - 3) + "...";
}
break;
}
// Adjust the column width
c.setWidth(value.length() > c.getWidth() ? value.length() : c.getWidth());
c.addValue(value);
} // END of for loop columnCount
rowCount++;
} // END of while (rs.next)
/*
At this point we have gone through meta data, get the
columns and created all Column objects, iterated over the
ResultSet rows, populated the column values and adjusted
the column widths.
We cannot start printing just yet because we have to prepare
a row separator String.
*/
// For the fun of it, I will use StringBuilder
StringBuilder strToPrint = new StringBuilder();
StringBuilder rowSeparator = new StringBuilder();
/*
Prepare column labels to print as well as the row separator.
It should look something like this:
+--------+------------+------------+-----------+ (row separator)
| EMP_NO | BIRTH_DATE | FIRST_NAME | LAST_NAME | (labels row)
+--------+------------+------------+-----------+ (row separator)
*/
// Iterate over columns
for (Column c : columns) {
int width = c.getWidth();
// Center the column label
String toPrint;
String name = c.getLabel();
int diff = width - name.length();
if ((diff % 2) == 1) {
// diff is not divisible by 2, add 1 to width (and diff)
// so that we can have equal padding to the left and right
// of the column label.
width++;
diff++;
c.setWidth(width);
}
int paddingSize = diff / 2; // InteliJ says casting to int is redundant.
// Cool String repeater code thanks to user102008 at stackoverflow.com
String padding = new String(new char[paddingSize]).replace("\0", " ");
toPrint = "| " + padding + name + padding + " ";
// END centering the column label
strToPrint.append(toPrint);
rowSeparator.append("+");
rowSeparator.append(new String(new char[width + 2]).replace("\0", "-"));
}
String lineSeparator = System.getProperty("line.separator");
// Is this really necessary ??
lineSeparator = lineSeparator == null ? "\n" : lineSeparator;
rowSeparator.append("+").append(lineSeparator);
strToPrint.append("|").append(lineSeparator);
strToPrint.insert(0, rowSeparator);
strToPrint.append(rowSeparator);
StringJoiner sj = new StringJoiner(", ");
for (String name : tableNames) {
sj.add(name);
}
String info = "Printing " + rowCount;
info += rowCount > 1 ? " rows from " : " row from ";
info += tableNames.size() > 1 ? "tables " : "table ";
info += sj.toString();
System.out.println(info);
// Print out the formatted column labels
System.out.print(strToPrint.toString());
String format;
// Print out the rows
for (int i = 0; i
* Integers should not be truncated so column widths should
* be adjusted without a column width limit. Text columns should be
* left justified and can be truncated to a max. column width etc...
*
* See also:
* java.sql.Types
*
* #param type Generic SQL type
* #return The category this type belongs to
*/
private static int whichCategory(int type) {
switch (type) {
case Types.BIGINT:
case Types.TINYINT:
case Types.SMALLINT:
case Types.INTEGER:
return CATEGORY_INTEGER;
case Types.REAL:
case Types.DOUBLE:
case Types.DECIMAL:
return CATEGORY_DOUBLE;
case Types.DATE:
case Types.TIME:
case Types.TIME_WITH_TIMEZONE:
case Types.TIMESTAMP:
case Types.TIMESTAMP_WITH_TIMEZONE:
return CATEGORY_DATETIME;
case Types.BOOLEAN:
return CATEGORY_BOOLEAN;
case Types.VARCHAR:
case Types.NVARCHAR:
case Types.LONGVARCHAR:
case Types.LONGNVARCHAR:
case Types.CHAR:
case Types.NCHAR:
return CATEGORY_STRING;
default:
return CATEGORY_OTHER;
}
}
/**
* Represents a database table column.
*/
private static class Column {
/**
* Column label.
*/
private String label;
/**
* Generic SQL type of the column as defined in
*
* java.sql.Types
* .
*/
private int type;
/**
* Generic SQL type name of the column as defined in
*
* java.sql.Types
* .
*/
private String typeName;
/**
* Width of the column that will be adjusted according to column label
* and values to be printed.
*/
private int width = 0;
/**
* Column values from each row of a ResultSet.
*/
private List values = new ArrayList();
/**
* Flag for text justification using String.format.
* Empty string ("") to justify right,
* dash (-) to justify left.
*
* #see #justifyLeft()
*/
private String justifyFlag = "";
/**
* Column type category. The columns will be categorised according
* to their column types and specific needs to print them correctly.
*/
private int typeCategory = 0;
/**
* Constructs a new Column with a column label,
* generic SQL type and type name (as defined in
*
* java.sql.Types
* )
*
* #param label Column label or name
* #param type Generic SQL type
* #param typeName Generic SQL type name
*/
public Column(String label, int type, String typeName) {
this.label = label;
this.type = type;
this.typeName = typeName;
}
/**
* Returns the column label
*
* #return Column label
*/
public String getLabel() {
return label;
}
/**
* Returns the generic SQL type of the column
*
* #return Generic SQL type
*/
public int getType() {
return type;
}
/**
* Returns the generic SQL type name of the column
*
* #return Generic SQL type name
*/
public String getTypeName() {
return typeName;
}
/**
* Returns the width of the column
*
* #return Column width
*/
public int getWidth() {
return width;
}
/**
* Sets the width of the column to width
*
* #param width Width of the column
*/
public void setWidth(int width) {
this.width = width;
}
/**
* Adds a String representation (value)
* of a value to this column object's {#link #values} list.
* These values will come from each row of a
*
* ResultSet
* of a database query.
*
* #param value The column value to add to {#link #values}
*/
public void addValue(String value) {
values.add(value);
}
/**
* Returns the column value at row index i.
* Note that the index starts at 0 so that getValue(0)
* will get the value for this column from the first row
* of a
* ResultSet.
*
* #param i The index of the column value to get
* #return The String representation of the value
*/
public String getValue(int i) {
return values.get(i);
}
/**
* Returns the value of the {#link #justifyFlag}. The column
* values will be printed using String.format and
* this flag will be used to right or left justify the text.
*
* #return The {#link #justifyFlag} of this column
* #see #justifyLeft()
*/
public String getJustifyFlag() {
return justifyFlag;
}
/**
* Sets {#link #justifyFlag} to "-" so that
* the column value will be left justified when printed with
* String.format. Typically numbers will be right
* justified and text will be left justified.
*/
public void justifyLeft() {
this.justifyFlag = "-";
}
/**
* Returns the generic SQL type category of the column
*
* #return The {#link #typeCategory} of the column
*/
public int getTypeCategory() {
return typeCategory;
}
/**
* Sets the {#link #typeCategory} of the column
*
* #param typeCategory The type category
*/
public void setTypeCategory(int typeCategory) {
this.typeCategory = typeCategory;
}
}
}
This is the scala version of doing this... which will print column names and data as well in a generic way...
def printQuery(res: ResultSet): Unit = {
val rsmd = res.getMetaData
val columnCount = rsmd.getColumnCount
var rowCnt = 0
val s = StringBuilder.newBuilder
while (res.next()) {
s.clear()
if (rowCnt == 0) {
s.append("| ")
for (i <- 1 to columnCount) {
val name = rsmd.getColumnName(i)
s.append(name)
s.append("| ")
}
s.append("\n")
}
rowCnt += 1
s.append("| ")
for (i <- 1 to columnCount) {
if (i > 1)
s.append(" | ")
s.append(res.getString(i))
}
s.append(" |")
System.out.println(s)
}
System.out.println(s"TOTAL: $rowCnt rows")
}

Have a look at the documentation. You made the following mistakes.
Firstly, ps.executeQuery() doesn't have any parameters. Instead you passed the SQL query into it.
Secondly, regarding the prepared statement, you have to use the ? symbol if want to pass any parameters. And later bind it using
setXXX(index, value)
Here xxx stands for the data type.

You can use the TableSaw library, which is a great Java data science / data frame library. The code is simple then:
System.out.println(Table.read().db(resultSet).print());

For what you are trying to do, instead of PreparedStatement you can use Statement. Your code may be modified as-
String sql = "SELECT column_name from information_schema.columns where table_name='suppliers';";
Statement s = connection.createStatement();
ResultSet rs = s.executeQuery(sql);
Hope this helps.

Solution with rowMapper impl.
Repository class:
jdbcTemplate.query(sqlRequest, new ResponseQuikRowMapper())
Row mapper class:
public class ResponseQuikRowMapper implements RowMapper<Map<String, String>> {
#Override
#SneakyThrows
public Map<String, String> mapRow(ResultSet rs, int rowNum) {
return IntStream.range(1, rs.getMetaData().getColumnCount())
.mapToObj(columnNumber -> getColumnName(rs, columnNumber))
.collect(Collectors.toMap(column -> column, value -> getColumnValue(rs, value)));
}
#SneakyThrows
private String getColumnName(ResultSet rs, Integer columnNumber) {
return rs.getMetaData().getColumnName(columnNumber);
}
#SneakyThrows
private String getColumnValue(ResultSet rs, String column) {
return Optional.ofNullable(rs.getString(column)).orElse("");
}
HashMap it`s simple matrix where key is column name and value is value :)

If you are using Spring data, you could try this:
var mapped = new ColumnMapRowMapper().mapRow(resultSet, rowNum);
log.debug("Result={}", mapped);

can't find source of inadvertent loop

I started refactoring this program I was working on and hit a major road block... I have one class that acts as a nucleus, with about 6 other smaller (but still important) classes working together to run the program... I took one method [called 'populate()'] out the nucleus class and made an entirely new class with it [called 'PopulationGenerator'], but when I try to create an object of the newly created class anywhere in the nucleus class I get stuck in a never ending loop of that new class
I've never had this issue when trying to create objects before... Here's the nucleus class before refactoring:
public class Simulator
{
// Constants representing configuration information for the simulation.
// The default width for the grid.
private static final int DEFAULT_WIDTH = 120;
// The default depth of the grid.
private static final int DEFAULT_DEPTH = 80;
// The probability that a fox will be created in any given grid position.
private static final double FOX_CREATION_PROBABILITY = 0.02;
// The probability that a rabbit will be created in any given grid position.
private static final double RABBIT_CREATION_PROBABILITY = 0.08;
// List of animals in the field.
private List<Animal> animals;
// The current state of the field.
private Field field;
// The current step of the simulation.
private int step;
// A graphical view of the simulation.
private SimulatorView view;
/**
* Construct a simulation field with default size.
*/
public Simulator()
{
this(DEFAULT_DEPTH, DEFAULT_WIDTH);
}
/**
* Create a simulation field with the given size.
* #param depth Depth of the field. Must be greater than zero.
* #param width Width of the field. Must be greater than zero.
*/
public Simulator(int depth, int width)
{
if(width <= 0 || depth <= 0) {
System.out.println("The dimensions must be greater than zero.");
System.out.println("Using default values.");
depth = DEFAULT_DEPTH;
width = DEFAULT_WIDTH;
}
animals = new ArrayList<Animal>();
field = new Field(depth, width);
// Create a view of the state of each location in the field.
view = new SimulatorView(depth, width);
view.setColor(Rabbit.class, Color.orange);
view.setColor(Fox.class, Color.blue);
// Setup a valid starting point.
reset();
}
/**
* Run the simulation from its current state for a reasonably long period,
* (4000 steps).
*/
public void runLongSimulation()
{
simulate(4000);
}
/**
* Run the simulation from its current state for the given number of steps.
* Stop before the given number of steps if it ceases to be viable.
* #param numSteps The number of steps to run for.
*/
public void simulate(int numSteps)
{
for(int step = 1; step <= numSteps && view.isViable(field); step++) {
simulateOneStep();
}
}
/**
* Run the simulation from its current state for a single step.
* Iterate over the whole field updating the state of each
* fox and rabbit.
*/
public void simulateOneStep()
{
step++;
// Provide space for newborn animals.
List<Animal> newAnimals = new ArrayList<Animal>();
// Let all rabbits act.
for(Iterator<Animal> it = animals.iterator(); it.hasNext(); ) {
Animal animal = it.next();
animal.act(newAnimals);
if(! animal.isAlive()) {
it.remove();
}
}
// Add the newly born foxes and rabbits to the main lists.
animals.addAll(newAnimals);
view.showStatus(step, field);
}
/**
* Reset the simulation to a starting position.
*/
public void reset()
{
step = 0;
animals.clear();
populate();
// Show the starting state in the view.
view.showStatus(step, field);
}
/**
* Randomly populate the field with foxes and rabbits.
*/
private void populate()
{
Random rand = Randomizer.getRandom();
field.clear();
for(int row = 0; row < field.getDepth(); row++) {
for(int col = 0; col < field.getWidth(); col++) {
if(rand.nextDouble() <= FOX_CREATION_PROBABILITY) {
Location location = new Location(row, col);
Fox fox = new Fox(true, field, location);
animals.add(fox);
}
else if(rand.nextDouble() <= RABBIT_CREATION_PROBABILITY) {
Location location = new Location(row, col);
Rabbit rabbit = new Rabbit(true, field, location);
animals.add(rabbit);
}
// else leave the location empty.
}
}
}
}
EDIT:
Here's this same class AFTER refactoring ...
import java.util.Random;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.awt.Color;
/**
* A simple predator-prey simulator, based on a rectangular field
* containing rabbits and foxes.
*
* Update 10.40:
* Now *almost* decoupled from the concrete animal classes.
*
* #TWiSTED_CRYSTALS
*/
public class Simulator
{
// Constants representing configuration information for the simulation.
// The default width for the grid.
private static final int DEFAULT_WIDTH = 120;
// The default depth of the grid.
private static final int DEFAULT_DEPTH = 80;
// The current state of the field.
private Field field;
// The current step of the simulation.
private int step;
// A graphical view of the simulation.
private SimulatorView view;
//Population Generator class... coupled to fox and rabbit classes
private PopulationGenerator popGenerator;
// Lists of animals in the field. Separate lists are kept for ease of iteration.
private List<Animal> animals;
/**
* Construct a simulation field with default size.
*/
public Simulator()
{
this(DEFAULT_DEPTH, DEFAULT_WIDTH);
}
/**
* Create a simulation field with the given size.
* #param depth Depth of the field. Must be greater than zero.
* #param width Width of the field. Must be greater than zero.
*/
public Simulator(int depth, int width)
{
if(width <= 0 || depth <= 0) {
System.out.println("The dimensions must be greater than zero.");
System.out.println("Using default values.");
depth = DEFAULT_DEPTH;
width = DEFAULT_WIDTH;
}
animals = new ArrayList<Animal>();
field = new Field(depth, width);
// Create a view of the state of each location in the field.
//
// view.setColor(Rabbit.class, Color.orange); // PG
// view.setColor(Fox.class, Color.blue); // PG
// Setup a valid starting point.
reset();
}
/**
* Run the simulation from its current state for a reasonably long period,
* (4000 steps).
*/
public void runLongSimulation()
{
simulate(4000);
}
/**
* Run the simulation from its current state for the given number of steps.
* Stop before the given number of steps if it ceases to be viable.
* #param numSteps The number of steps to run for.
*/
public void simulate(int numSteps)
{
for(int step = 1; step <= numSteps && view.isViable(field); step++) {
simulateOneStep();
}
}
/**
* Run the simulation from its current state for a single step.
* Iterate over the whole field updating the state of each
* fox and rabbit.
*/
public void simulateOneStep()
{
step++;
// Provide space for animals.
List<Animal> newAnimals = new ArrayList<Animal>();
// Let all animals act.
for(Iterator<Animal> it = animals.iterator(); it.hasNext(); ) {
Animal animal = it.next();
animal.act(newAnimals);
if(! animal.isAlive()) {
it.remove();
}
}
animals.addAll(newAnimals);
}
/**
* Reset the simulation to a starting position.
*/
public void reset()
{
PopulationGenerator popGenerator = new PopulationGenerator();
step = 0;
animals.clear();
popGenerator.populate();
// Show the starting state in the view.
view.showStatus(step, field);
}
public int getStep()
{
return step;
}
}
... and the new class
import java.util.ArrayList;
import java.util.Random;
import java.util.List;
import java.awt.Color;
public class PopulationGenerator
{
// The default width for the grid.
private static final int DEFAULT_WIDTH = 120;
// The default depth of the grid.
private static final int DEFAULT_DEPTH = 80;
// The probability that a fox will be created in any given grid position.
private static final double FOX_CREATION_PROBABILITY = 0.02;
// The probability that a rabbit will be created in any given grid position.
private static final double RABBIT_CREATION_PROBABILITY = 0.08;
// Lists of animals in the field. Separate lists are kept for ease of iteration.
private List<Animal> animals;
// The current state of the field.
private Field field;
// A graphical view of the simulation.
private SimulatorView view;
/**
* Constructor
*/
public PopulationGenerator()
{
animals = new ArrayList<Animal>();
field = new Field(DEFAULT_DEPTH, DEFAULT_WIDTH);
}
/**
* Randomly populate the field with foxes and rabbits.
*/
public void populate()
{
// Create a view of the state of each location in the field.
view = new SimulatorView(DEFAULT_DEPTH, DEFAULT_WIDTH);
view.setColor(Rabbit.class, Color.orange); // PG
view.setColor(Fox.class, Color.blue); // PG
Simulator simulator = new Simulator();
Random rand = Randomizer.getRandom();
field.clear();
for(int row = 0; row < field.getDepth(); row++) {
for(int col = 0; col < field.getWidth(); col++) {
if(rand.nextDouble() <= FOX_CREATION_PROBABILITY) {
Location location = new Location(row, col);
Fox fox = new Fox(true, field, location);
animals.add(fox);
}
else if(rand.nextDouble() <= RABBIT_CREATION_PROBABILITY) {
Location location = new Location(row, col);
Rabbit rabbit = new Rabbit(true, field, location);
animals.add(rabbit);
}
// else leave the location empty.
}
}
view.showStatus(simulator.getStep(), field);
}
}
here's the Field class that the PopulationGenerator calls... I havent changed this class in any way
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Random;
/**
* Represent a rectangular grid of field positions.
* Each position is able to store a single animal.
*
* #TWiSTED_CRYSTALS
*/
public class Field
{
// A random number generator for providing random locations.
private static final Random rand = Randomizer.getRandom();
// The depth and width of the field.
private int depth, width;
// Storage for the animals.
private Object[][] field;
/**
* Represent a field of the given dimensions.
* #param depth The depth of the field.
* #param width The width of the field.
*/
public Field(int depth, int width)
{
this.depth = depth;
this.width = width;
field = new Object[depth][width];
}
/**
* Empty the field.
*/
public void clear()
{
for(int row = 0; row < depth; row++) {
for(int col = 0; col < width; col++) {
field[row][col] = null;
}
}
}
/**
* Clear the given location.
* #param location The location to clear.
*/
public void clear(Location location)
{
field[location.getRow()][location.getCol()] = null;
}
/**
* Place an animal at the given location.
* If there is already an animal at the location it will
* be lost.
* #param animal The animal to be placed.
* #param row Row coordinate of the location.
* #param col Column coordinate of the location.
*/
public void place(Object animal, int row, int col)
{
place(animal, new Location(row, col));
}
/**
* Place an animal at the given location.
* If there is already an animal at the location it will
* be lost.
* #param animal The animal to be placed.
* #param location Where to place the animal.
*/
public void place(Object animal, Location location)
{
field[location.getRow()][location.getCol()] = animal;
}
/**
* Return the animal at the given location, if any.
* #param location Where in the field.
* #return The animal at the given location, or null if there is none.
*/
public Object getObjectAt(Location location)
{
return getObjectAt(location.getRow(), location.getCol());
}
/**
* Return the animal at the given location, if any.
* #param row The desired row.
* #param col The desired column.
* #return The animal at the given location, or null if there is none.
*/
public Object getObjectAt(int row, int col)
{
return field[row][col];
}
/**
* Generate a random location that is adjacent to the
* given location, or is the same location.
* The returned location will be within the valid bounds
* of the field.
* #param location The location from which to generate an adjacency.
* #return A valid location within the grid area.
*/
public Location randomAdjacentLocation(Location location)
{
List<Location> adjacent = adjacentLocations(location);
return adjacent.get(0);
}
/**
* Get a shuffled list of the free adjacent locations.
* #param location Get locations adjacent to this.
* #return A list of free adjacent locations.
*/
public List<Location> getFreeAdjacentLocations(Location location)
{
List<Location> free = new LinkedList<Location>();
List<Location> adjacent = adjacentLocations(location);
for(Location next : adjacent) {
if(getObjectAt(next) == null) {
free.add(next);
}
}
return free;
}
/**
* Try to find a free location that is adjacent to the
* given location. If there is none, return null.
* The returned location will be within the valid bounds
* of the field.
* #param location The location from which to generate an adjacency.
* #return A valid location within the grid area.
*/
public Location freeAdjacentLocation(Location location)
{
// The available free ones.
List<Location> free = getFreeAdjacentLocations(location);
if(free.size() > 0) {
return free.get(0);
}
else {
return null;
}
}
/**
* Return a shuffled list of locations adjacent to the given one.
* The list will not include the location itself.
* All locations will lie within the grid.
* #param location The location from which to generate adjacencies.
* #return A list of locations adjacent to that given.
*/
public List<Location> adjacentLocations(Location location)
{
assert location != null : "Null location passed to adjacentLocations";
// The list of locations to be returned.
List<Location> locations = new LinkedList<Location>();
if(location != null) {
int row = location.getRow();
int col = location.getCol();
for(int roffset = -1; roffset <= 1; roffset++) {
int nextRow = row + roffset;
if(nextRow >= 0 && nextRow < depth) {
for(int coffset = -1; coffset <= 1; coffset++) {
int nextCol = col + coffset;
// Exclude invalid locations and the original location.
if(nextCol >= 0 && nextCol < width && (roffset != 0 || coffset != 0)) {
locations.add(new Location(nextRow, nextCol));
}
}
}
}
// Shuffle the list. Several other methods rely on the list
// being in a random order.
Collections.shuffle(locations, rand);
}
return locations;
}
/**
* Return the depth of the field.
* #return The depth of the field.
*/
public int getDepth()
{
return depth;
}
/**
* Return the width of the field.
* #return The width of the field.
*/
public int getWidth()
{
return width;
}
}

your problem is not in the Field class but below it. The Simulator constructor calls reset() which creates a new PopulationGenerator object, then calls populate() on that object. The populate() method calls Simulator simulator = new Simulator(); which creates a new Simulator object which continues the cycle. Solution: don't create a new Simulator object in PopulationGenerator, but instead pass the existing simulator to PopulationGenerator through its constructor or through a setSimulator(...) method.
e.g.,
class PopulationGenerator {
// ... etc...
private Simulator simulator; // null to begin with
// pass Simulator instance into constructor.
// Probably will need to do the same with SimulatorView
public PopulationGenerator(Simulator simulator, int depth, int width) {
this.simulator = simulator; // set the instance
// ... more code etc...
}
public void populate() {
// don't re-create Simulator here but rather use the instance passed in
}
}

UnsatisfiedLinkError: How to create an unsynchronized deflater?

I would like to create a version of Java's deflater not synchronizing on its ZStreamRef instance.
I started by copying the code into a Deflater2 class. The code compiles, however, when I create an instance of that class, I get:
Exception in thread "main" java.lang.UnsatisfiedLinkError: net.dwst.bricolo.ResetGZip.Deflater2.initIDs()V
at net.mypackage.Deflater2.initIDs(Native Method)
at net.mypackage.Deflater2.<clinit>(Deflater2.java:65)
at net.mypackage.SpeedTest.main(SpeedTest.java:13)
How can I create an instance of Deflater2 without triggering this exception?
I am providing the code for Deflater2:
package net.mypackage;
public class Deflater2 {
private final ZStreamRef zsRef;
private byte[] buf = new byte[0];
private int off, len;
private int level, strategy;
private boolean setParams;
private boolean finish, finished;
/**
* Compression method for the deflate algorithm (the only one currently
* supported).
*/
public static final int DEFLATED = 8;
/**
* Compression level for no compression.
*/
public static final int NO_COMPRESSION = 0;
/**
* Compression level for fastest compression.
*/
public static final int BEST_SPEED = 1;
/**
* Compression level for best compression.
*/
public static final int BEST_COMPRESSION = 9;
/**
* Default compression level.
*/
public static final int DEFAULT_COMPRESSION = -1;
/**
* Compression strategy best used for data consisting mostly of small
* values with a somewhat random distribution. Forces more Huffman coding
* and less string matching.
*/
public static final int FILTERED = 1;
/**
* Compression strategy for Huffman coding only.
*/
public static final int HUFFMAN_ONLY = 2;
/**
* Default compression strategy.
*/
public static final int DEFAULT_STRATEGY = 0;
static {
/* Zip library is loaded from System.initializeSystemClass */
initIDs();
}
/**
* Creates a new compressor using the specified compression level.
* If 'nowrap' is true then the ZLIB header and checksum fields will
* not be used in order to support the compression format used in
* both GZIP and PKZIP.
* #param level the compression level (0-9)
* #param nowrap if true then use GZIP compatible compression
*/
public Deflater2(int level, boolean nowrap) {
this.level = level;
this.strategy = DEFAULT_STRATEGY;
this.zsRef = new ZStreamRef(init(level, DEFAULT_STRATEGY, nowrap));
}
/**
* Creates a new compressor using the specified compression level.
* Compressed data will be generated in ZLIB format.
* #param level the compression level (0-9)
*/
public Deflater2(int level) {
this(level, false);
}
/**
* Creates a new compressor with the default compression level.
* Compressed data will be generated in ZLIB format.
*/
public Deflater2() {
this(DEFAULT_COMPRESSION, false);
}
/**
* Sets input data for compression. This should be called whenever
* needsInput() returns true indicating that more input data is required.
* #param b the input data bytes
* #param off the start offset of the data
* #param len the length of the data
* #see Deflater#needsInput
*/
public void setInput(byte[] b, int off, int len) {
if (b== null) {
throw new NullPointerException();
}
if (off < 0 || len < 0 || off > b.length - len) {
throw new ArrayIndexOutOfBoundsException();
}
synchronized (zsRef) {
this.buf = b;
this.off = off;
this.len = len;
}
}
/**
* Sets input data for compression. This should be called whenever
* needsInput() returns true indicating that more input data is required.
* #param b the input data bytes
* #see Deflater#needsInput
*/
public void setInput(byte[] b) {
setInput(b, 0, b.length);
}
/**
* Sets preset dictionary for compression. A preset dictionary is used
* when the history buffer can be predetermined. When the data is later
* uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
* in order to get the Adler-32 value of the dictionary required for
* decompression.
* #param b the dictionary data bytes
* #param off the start offset of the data
* #param len the length of the data
* #see Inflater#inflate
* #see Inflater#getAdler
*/
public void setDictionary(byte[] b, int off, int len) {
if (b == null) {
throw new NullPointerException();
}
if (off < 0 || len < 0 || off > b.length - len) {
throw new ArrayIndexOutOfBoundsException();
}
synchronized (zsRef) {
ensureOpen();
setDictionary(zsRef.address(), b, off, len);
}
}
/**
* Sets preset dictionary for compression. A preset dictionary is used
* when the history buffer can be predetermined. When the data is later
* uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
* in order to get the Adler-32 value of the dictionary required for
* decompression.
* #param b the dictionary data bytes
* #see Inflater#inflate
* #see Inflater#getAdler
*/
public void setDictionary(byte[] b) {
setDictionary(b, 0, b.length);
}
/**
* Sets the compression strategy to the specified value.
* #param strategy the new compression strategy
* #exception IllegalArgumentException if the compression strategy is
* invalid
*/
public void setStrategy(int strategy) {
switch (strategy) {
case DEFAULT_STRATEGY:
case FILTERED:
case HUFFMAN_ONLY:
break;
default:
throw new IllegalArgumentException();
}
synchronized (zsRef) {
if (this.strategy != strategy) {
this.strategy = strategy;
setParams = true;
}
}
}
/**
* Sets the current compression level to the specified value.
* #param level the new compression level (0-9)
* #exception IllegalArgumentException if the compression level is invalid
*/
public void setLevel(int level) {
if ((level < 0 || level > 9) && level != DEFAULT_COMPRESSION) {
throw new IllegalArgumentException("invalid compression level");
}
synchronized (zsRef) {
if (this.level != level) {
this.level = level;
setParams = true;
}
}
}
/**
* Returns true if the input data buffer is empty and setInput()
* should be called in order to provide more input.
* #return true if the input data buffer is empty and setInput()
* should be called in order to provide more input
*/
public boolean needsInput() {
return len <= 0;
}
/**
* When called, indicates that compression should end with the current
* contents of the input buffer.
*/
public void finish() {
synchronized (zsRef) {
finish = true;
}
}
/**
* Returns true if the end of the compressed data output stream has
* been reached.
* #return true if the end of the compressed data output stream has
* been reached
*/
public boolean finished() {
synchronized (zsRef) {
return finished;
}
}
/**
* Fills specified buffer with compressed data. Returns actual number
* of bytes of compressed data. A return value of 0 indicates that
* needsInput() should be called in order to determine if more input
* data is required.
* #param b the buffer for the compressed data
* #param off the start offset of the data
* #param len the maximum number of bytes of compressed data
* #return the actual number of bytes of compressed data
*/
public int deflate(byte[] b, int off, int len) {
if (b == null) {
throw new NullPointerException();
}
if (off < 0 || len < 0 || off > b.length - len) {
throw new ArrayIndexOutOfBoundsException();
}
synchronized (zsRef) {
ensureOpen();
return deflateBytes(zsRef.address(), b, off, len);
}
}
/**
* Fills specified buffer with compressed data. Returns actual number
* of bytes of compressed data. A return value of 0 indicates that
* needsInput() should be called in order to determine if more input
* data is required.
* #param b the buffer for the compressed data
* #return the actual number of bytes of compressed data
*/
public int deflate(byte[] b) {
return deflate(b, 0, b.length);
}
/**
* Returns the ADLER-32 value of the uncompressed data.
* #return the ADLER-32 value of the uncompressed data
*/
public int getAdler() {
synchronized (zsRef) {
ensureOpen();
return getAdler(zsRef.address());
}
}
/**
* Returns the total number of uncompressed bytes input so far.
*
* <p>Since the number of bytes may be greater than
* Integer.MAX_VALUE, the {#link #getBytesRead()} method is now
* the preferred means of obtaining this information.</p>
*
* #return the total number of uncompressed bytes input so far
*/
public int getTotalIn() {
return (int) getBytesRead();
}
/**
* Returns the total number of uncompressed bytes input so far.</p>
*
* #return the total (non-negative) number of uncompressed bytes input so far
* #since 1.5
*/
public long getBytesRead() {
synchronized (zsRef) {
ensureOpen();
return getBytesRead(zsRef.address());
}
}
/**
* Returns the total number of compressed bytes output so far.
*
* <p>Since the number of bytes may be greater than
* Integer.MAX_VALUE, the {#link #getBytesWritten()} method is now
* the preferred means of obtaining this information.</p>
*
* #return the total number of compressed bytes output so far
*/
public int getTotalOut() {
return (int) getBytesWritten();
}
/**
* Returns the total number of compressed bytes output so far.</p>
*
* #return the total (non-negative) number of compressed bytes output so far
* #since 1.5
*/
public long getBytesWritten() {
synchronized (zsRef) {
ensureOpen();
return getBytesWritten(zsRef.address());
}
}
/**
* Resets deflater so that a new set of input data can be processed.
* Keeps current compression level and strategy settings.
*/
public void reset() {
synchronized (zsRef) {
ensureOpen();
reset(zsRef.address());
finish = false;
finished = false;
off = len = 0;
}
}
/**
* Closes the compressor and discards any unprocessed input.
* This method should be called when the compressor is no longer
* being used, but will also be called automatically by the
* finalize() method. Once this method is called, the behavior
* of the Deflater object is undefined.
*/
public void end() {
synchronized (zsRef) {
long addr = zsRef.address();
zsRef.clear();
if (addr != 0) {
end(addr);
buf = null;
}
}
}
/**
* Closes the compressor when garbage is collected.
*/
protected void finalize() {
end();
}
private void ensureOpen() {
assert Thread.holdsLock(zsRef);
if (zsRef.address() == 0)
throw new NullPointerException("Deflater has been closed");
}
private static native void initIDs();
private native static long init(int level, int strategy, boolean nowrap);
private native static void setDictionary(long addr, byte[] b, int off,
int len);
private native int deflateBytes(long addr, byte[] b, int off, int len);
private native static int getAdler(long addr);
private native static long getBytesRead(long addr);
private native static long getBytesWritten(long addr);
private native static void reset(long addr);
private native static void end(long addr);
}

Your problem is not in java code.
There can be the following reasons:
the library that you are using or other library that your library depends on is not in library path (java.library.path option)
One of the native libraries you try to use does not match your platforms. For example you are running on 32 bit platform and trying to use 64bit library.
Take a look here: How to add native library to "java.library.path" with Eclipse launch (instead of overriding it)