Develop Reference

sorting files using multithreading in java

I was given an assignment to write all ordered contents of given files into a result.txt. At first, the filenames are split into different Arraylists where each file contains a label in a format #n/N where N is the total number of files. e.g.
British explorer James Clark Ross led the first
expedition to reach the north magnetic pole
#001/004
from a file 1831-06-01.txt
The problem with my code is that it has written in order 1,4,2,3 respectively. However, the result must be in order 1,2,3,4. This may be due to a lack of synchronization. Nonetheless, I am still struggling to fix the problem.
This is my code:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.*;
class PopThread implements Runnable {
ArrayList<String> fileList;
public PopThread(ArrayList<String> fileList) {
this.fileList = fileList;
}
#Override
public void run() {
//System.out.println("running\n");
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
long startTime = System.nanoTime();
System.out.println("fileList: " + fileList);
ArrayList<String> sortedFileList = sortFiles(fileList);
File resultFile = new File("result.txt");
for (String filename : sortedFileList) {
Writer w1 = new Writer(filename, resultFile);
Thread t = new Thread(w1);
t.setPriority(Thread.MAX_PRIORITY);
t.start();
}
long stopTime = System.nanoTime();
//System.out.println("Total execution time: " + (stopTime - startTime));
}
public ArrayList<String> readFiles(String filename) {
ArrayList<String> list = new ArrayList<String>();
try {
File myObj = new File(filename);
Scanner s = new Scanner(myObj);
while (s.hasNext()) {
list.add(s.next());
}
s.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return list;
}
public int getNumber(String filename) {
String lastLine = "";
String sCurrentLine;
int identifier_integer = -1;
try {
BufferedReader br = new BufferedReader(new FileReader(filename));
while ((sCurrentLine = br.readLine()) != null) {
lastLine = sCurrentLine;
}
String identifier_number = lastLine.substring(1,4);
identifier_integer = Integer.parseInt(identifier_number);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
return identifier_integer;
}
public ArrayList<String> sortFiles(ArrayList<String> listFileName) {
int i = listFileName.size();
boolean sorted = false;
while ( (i > 1) && (!(sorted)) ) {
sorted = true;
for (int j = 1; j < i; j++) {
if ( getNumber(listFileName.get(j-1)) > getNumber(listFileName.get(j)) ) {
String temp = listFileName.get(j-1);
listFileName.set(j-1, listFileName.get(j));
listFileName.set(j, temp);
sorted = false;
}
}
i--;
}
return listFileName;
}
}
class Writer implements Runnable {
String filename;
File resultFile;
public Writer(String filename, File resultFile) {
this.filename = filename;
this.resultFile = resultFile;
}
#Override
public void run() {
String content;
content = readFromFile(filename);
writeToFile(resultFile, content);
}
private static void writeToFile(File resultFile, String content) {
try {
BufferedWriter writer = new BufferedWriter(new FileWriter(resultFile, true));
writer.write(content);
//writer.write("file content written");
writer.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
static String readFromFile(String filename) {
StringBuffer content = new StringBuffer();
try {
String text;
BufferedReader reader = new BufferedReader(new FileReader(filename));
while ((text = reader.readLine()) != null) {
content.append(text);
content.append("\n");
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
return content.toString();
}
}
public class q4 {
public static void main(String[] args) {
ArrayList<String> filesOne = new ArrayList<String>();
filesOne.add("1831-06-01.txt");
filesOne.add("2003-08-27.txt");
ArrayList<String> filesTwo = new ArrayList<String>();
filesTwo.add("1961-04-12.txt");
filesTwo.add("1972-12-11.txt");
PopThread popRunnableOne = new PopThread(filesOne);
PopThread popRunnableTwo = new PopThread(filesTwo);
Thread threadOne = new Thread(popRunnableOne);
Thread threadTwo = new Thread(popRunnableTwo);
threadOne.start();
threadTwo.start();
try {
threadOne.join();
threadTwo.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
( NOTE: The class q4 cannot be altered)

This assignment is horrible. You have my sympathy.
Your two threads will have to communicate with each other. Each thread will have to know, what is the filename that the other thread wants to output next. And, they will have to take turns. Each thread needs to loop:
While the date on my next file is less than or equal to the date on the other thread's next file, output my next file,
Tell the other thread, "it's your turn,"
If I have no more files, then exit (return from the run() method), otherwise, wait for the other thread to tell me it's my turn again,
Go back to step 1.
Having to take turns is the worst part of the assignment. Any time you find yourself needing to make threads take turns doing something—any time you need to make threads do things in a particular order—that's a clear sign that all of the things should be done by a single thread.
The only way threads can communicate is through shared variables. Your instructor has done you a huge disservice by telling you not to modify the q4 class. That prevents you from passing any shared objects in to your PopThread implementation through its constructor.
The only other way your two threads can share any variables is by making the variables static. Forcing you to use static is the second worst part of the assignment. If you go on to study software engineering, you will learn that static is an anti-pattern. Programs that use static variables are brittle (i.e., hard to modify), and they are hard to test.
Forcing you to use static variables also will make your threads do extra work to figure out who is who. Normally, I would do something like this so that each thread would automatically know which state is its own, and which belongs to the other guy:
class SharedState { ... }
class PopThread {
public PopThread(
SharedState myState,
SharedState otherThreadState,
ArrayList<String> fileList
) {
this.myState = myState;
this.otherGuyState = otherThreadState;
this.fileList = fileList;
...initialize this.myState...
}
...
}
class q4 {
public static void main(String[] args) {
SharedState stateOne = new SharedState();
SharedState stateTwo = new SharedState();
PopThread popRunnableOne = new PopThread(stateOne, stateTwo, filesOne);
PopThread popRunnableTwo = new PopThread(stateTwo, stateOne, filesTwo);
...
}
}
The best way I can think of with static variables would be to have an array of two SharedState, and have the threads use an AtomicInteger to each assign themself one of the two array slots:
class PopThread {
static SharedState[] state = new SharedState [2];
static AtomicInteger nextStateIndex = new AtomicInteger(0);
public PopThread(
SharedState myState,
SharedState otherThreadState,
ArrayList<String> fileList
) {
myStateIndex = nextStateIndex.getAndIncrement();
otherGuysStateIndex = myStateIndex ^ 1;
this.fileList = fileList;
...initialize state[myStateIndex]...
}
...
}

Java: My ArrayList empties itself as soon as I empty the text file from which the ArrayList gets its contents

I´m writing my own library in java, where you can save variables very simple. But I have a problem in changing the values of the variables. The ArrayList empties itself as soon as the txt file is empty.
My Code:
public class SaveGameWriter {
private File file;
private boolean closed = false;
public void write(SaveGameFile savegamefile, String variableName, String variableValue, SaveGameReader reader) throws FileNotFoundException
{
if(!reader.read(savegamefile).contains(variableName))
{
file = savegamefile.getFile();
OutputStream stream = new FileOutputStream(file, true);
try {
String text = variableName+"="+variableValue;
stream.write(text.getBytes());
String lineSeparator = System.getProperty("line.separator");
stream.write(lineSeparator.getBytes());
}catch(IOException e)
{}
do {
try {
stream.close();
closed = true;
} catch (Exception e) {
closed = false;
}
} while (!closed);
}
}
public void setValueOf(SaveGameFile savegamefile, String variableName, String Value, SaveGameReader reader) throws IOException
{
ArrayList<String> list = reader.read(savegamefile);
if(list.contains(variableName))
{
list.set(list.indexOf(variableName), Value);
savegamefile.clear();
for(int i = 0; i<list.size()-1;i+=2)
{
write(savegamefile,list.get(i),list.get(i+1),reader);
}
}
}
}
Here my SaveGameReader class:
public class SaveGameReader {
private File file;
private ArrayList<String> result = new ArrayList<>();
public String getValueOf(SaveGameFile savegamefile, String variableName)
{
ArrayList<String> list = read(savegamefile);
if(list.contains(variableName))
{
return list.get(list.indexOf(variableName)+1);
}else
return null;
}
public ArrayList<String> read(SaveGameFile savegamefile) {
result.clear();
file = savegamefile.getFile();
BufferedReader in = null;
try {
in = new BufferedReader(new FileReader(file));
String read = null;
while ((read = in.readLine()) != null) {
String[] splited = read.split("=");
for (String part : splited) {
result.add(part);
}
}
} catch (IOException e) {
} finally {
boolean closed = false;
while(!closed)
{
try {
in.close();
closed=true;
} catch (Exception e) {
closed=false;
}
}
}
result.remove("");
return result;
}
}
And my SaveGameFile class:
public class SaveGameFile {
private File file;
public void create(String destination, String filename) throws IOException {
file = new File(destination+"/"+filename+".savegame");
if(!file.exists())
{
file.createNewFile();
}
}
public File getFile() {
return file;
}
public void clear() throws IOException
{
PrintWriter pw = new PrintWriter(file.getPath());
pw.close();
}
}
So, when I call the setValueOf() methode the ArrayList is empty and in the txt file there´s just the first variable + value. Hier´s my data structure:
Name=Testperson
Age=40
Phone=1234
Money=1000
What´s the problem with my code?

In your SaveGameReader.read() method you have result.clear(); which clears ArrayList. And you do it even before opening the file. So basically before every read from file operation you are cleaning up existing state and reread from file. If file is empty then you finish with empty list

Java parse csv class

I am making a class in java to parse in CSV's. It will read in the file line by line and parse out each field according to the regex pattern into an array, and then print that array. I put all this together in a main driver below. I looked over everything and it seems to be functional but for some reason whenever I run it, it just gets stuck in an infinite loop and will not cease. I have looked over this many times and can just not find where this would happen. Any help with this issue would be greatly appreciated!
import java.io.FileInputStream;
import java.io.IOException;
import java.util.regex.Pattern;
/**
*
*/
public class Csv {
private FileInputStream fin;
private String line;
private String[] parsedFields;
public boolean isEOL(char n) {
boolean eol;
if (n == '\n' || n == '\r') {
eol = true;
}
else
eol=false;
return eol;
}
public String getLine()
{
try
{
char c;
c= (char) fin.read();
while(!isEOL(c))
{
line+=c;
}
}
catch (IOException e) {
System.out.println("Input Error.");
}
return line;
}
public void parseFields(String s)
{
Pattern CSVLine=Pattern.compile("\"([^\"]*)\"|(?<=,|^)([^,]*)(?:,|$)");
parsedFields=CSVLine.split(s);
}
public void execute()
{
String field=getLine();
parseFields(field);
}
public void setFin(FileInputStream usrFin)
{
fin=usrFin;
}
public void outputFields()
{
for(int i=0; i<parsedFields.length;i++)
{
System.out.println(parsedFields[i]);
}
}
public static void main(String args[])
{
try {
FileInputStream fis;
fis = new FileInputStream("test.txt");
Csv test= new Csv();
test.setFin(fis);
test.execute();
test.outputFields();
}
catch (IOException e) {
e.printStackTrace();
}
}
}

c= (char) fin.read();
while(!isEOL(c))
{
line+=c;
}
In this part, you loop, adding c, but you never read again. c never changes during the loop, and probably is stuck there. You need to have the c = fin.read(); inside the loop too.

public static List<String> readLine(String filePath){
List<String> listStr = new ArrayList<String>();
try {
BufferedReader br = new BufferedReader(new FileReader(filePath));
String line = null;
Pattern pat = Pattern.compile(LINE_PATTERN_REGEXP);
while((line=br.readLine())!=null){
Matcher matcher = pat.matcher(line);
if(!matcher.find()){
listStr.add(line);
}
}
br.close();
} catch (IOException e) {
throw new RuntimeException(e);
}
return listStr;
}
}

How can i return an array in java that is accessible by other objects?

I want to return an array that is accessible by other objects after having read a text file. My instruction parsing class is:
import java.io.*;
public class Instruction {
public String[] instructionList;
public String[] readFile() throws IOException {
FileInputStream in = new FileInputStream("directions.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(in));
int n = 5;
instructionList = new String[n];
for (int j = 0; j < instructionList.length; j++) {
instructionList[j] = br.readLine();
}
in.close();
return instructionList;
}
}
The above takes in a text file with 5 lines of text in it. In my main() I want to run that function and have the string array be accessible to other objects.
import java.util.Arrays;
public class RoverCommand {
public static void main(String[] args) throws Exception {
Instruction directions = new Instruction();
directions.readFile();
String[] directionsArray;
directionsArray = directions.returnsInstructionList();
System.out.println(Arrays.toString(directionsArray));
}
}
What's the best way to do that? I would need the elements of the array to be integers if they are numbers and strings if they are letters. P.S. I'm brand new to Java. is there a better way to do what I'm doing?

You don't have to use generics. I try to catch exceptions in the accessors and return null if anything blows up. So you can test if the value returned is null before proceeding.
// Client.java
import java.io.IOException;
public class Client {
public static void main(String args[]) {
try {
InstructionList il = new InstructionList();
il.readFile("C:\\testing\\ints.txt", 5);
int[] integers = il.getInstructionsAsIntegers();
if (integers != null) {
for (int i : integers) {
System.out.println(i);
}
}
} catch (IOException e) {
// handle
}
}
}
// InstructionList.java
import java.io.*;
public class InstructionList {
private String[] instructions;
public void readFile(String path, int lineLimit) throws IOException {
FileInputStream in = new FileInputStream(path);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
instructions = new String[lineLimit];
for (int i = 0; i < lineLimit; i++) {
instructions[i] = br.readLine();
}
in.close();
}
public String[] getInstructionsAsStrings() {
return instructions; // will return null if uninitialized
}
public int[] getInstructionsAsIntegers() {
if (this.instructions == null) {
return null;
}
int[] instructions = new int[this.instructions.length];
try {
for (int i = 0; i < instructions.length; i++) {
instructions[i] = new Integer(this.instructions[i]);
}
} catch (NumberFormatException e) {
return null; // data integrity fail, return null
}
return instructions;
}
}

check instructionList is null or not. if it is null, call readFile method.
public String[] returnsInstructionList() {
if (instructionList== null){
try { readFile(); } catch(Exception e){}
}
return instructionList;
}
because of readFile can throw exception, it would be good to use one extra variable. like:
private boolean fileReaded = false;
public String[] returnsInstructionList() {
if (!fileReaded){
fileReaded = true;
try { readFile(); } catch(Exception e){}
}
return instructionList;
}
and if readFile can be run concurrently, easiest way to make function synchronized, like
private boolean fileReaded = false;
public synchronized void readFile() throws IOException {
.
.
.
}
public synchronized String[] returnsInstructionList() {
if (!fileReaded){
fileReaded = true;
try { readFile(); } catch(Exception e){}
}
return instructionList;
}

There is no guarantee that readFile is called before returnsInstructionList is invoked. Leaving you returnsInstructionList returning null.
I would :
public String[] getContentsFromFile(String fileName) throws IOException {
FileInputStream in = new FileInputStream(fileName);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
int n = 5;
instructionList = new String[n];
for (int j = 0; j < instructionList.length; j++) {
instructionList[j] = br.readLine();
}
in.close();
return instructionList;
}
Part two to the question you can use generics. To achieve what you want but you have to incorporate a way to say what it is.
Eg
public class Foo {
public ReturnForFoo returnAStringOrIntger(boolean val) {
if(val){
return new ReturnForFoo("String", ValueType.STRING) ;
}
return new ReturnForFoo(10, ValueType.INTEGER); //int
}
}
public class ReturnForFoo {
Object value;
ValueType type;
public ReturnForFoo(Object value, ValueType type) {
this.value=value;
this.type=type
}
// Asume you have getters for both value and value type
public static ENUM ValueType {
STRING,
INTEGER,
UNKNOWN
}
}
This code is in your main.
Foo foo = new Foo();
String value;
int val;
ReturnForFoo returnForFoo = foo.returnAStringOrIntger(true);
// NOTE you can use switch instead of if's and else if's. It will be better
if(returnForFoo.getValueType().equals(ValueType.INTEGER)){
val = (int) returnForFoo.getValue();
} else if(returnForFoo.getValueType().equals(ValueType.STRING)){
value = (String) returnForFoo.getValue();
} else {
// UNKOWN Case
}

Sorting lines in a file by 2 fields with JAVA

I work at a printing company that has many programs in COBOL and I have been tasked to
convert the COBOL programs into JAVA programs. I've run into a snag in the one conversion. I need to take a file that each line is a record and on each line the data is blocked.
Example of a line is
60000003448595072410013 FFFFFFFFFFV 80 0001438001000014530020120808060134
I need to sort data by a 5 digit number at the 19-23 characters and then by the very first character on a line.
BufferedReader input;
BufferedWriter output;
String[] sort, sorted, style, accountNumber, customerNumber;
String holder;
int lineCount;
int lineCounter() {
int result = 0;
boolean eof = false;
try {
FileReader inputFile = new FileReader("C:\\Users\\cbook\\Desktop\\Chemical\\"
+ "LB26529.fil");
input = new BufferedReader(inputFile);
while (!eof) {
holder = input.readLine();
if (holder == null) {
eof = true;
} else {
result++;
}
}
} catch (IOException e) {
System.out.println("Error - " + e.toString());
}
return result;
}
chemSort(){
lineCount = this.lineCounter();
sort = new String[lineCount];
sorted = new String[lineCount];
style = new String[lineCount];
accountNumber = new String[lineCount];
customerNumber = new String[lineCount];
try {
FileReader inputFile = new FileReader("C:\\Users\\cbook\\Desktop\\Chemical\\"
+ "LB26529.fil");
input = new BufferedReader(inputFile);
for (int i = 0; i < (lineCount + 1); i++) {
holder = input.readLine();
if (holder != null) {
sort[i] = holder;
style[i] = sort[i].substring(0, 1);
customerNumber[i] = sort[i].substring(252, 257);
}
}
} catch (IOException e) {
System.out.println("Error - " + e.toString());
}
}
This what I have so far and I'm not really sure where to go from here or even if this is the correct way
to go about sorting the file. After the file is sorted it will be stored into another file and processed
again with another program for it to be ready for printing.

List<String> linesAsList = new ArrayList<String>();
String line=null;
while(null!=(line=reader.readLine())) linesAsList.add(line);
Collections.sort(linesAsList, new Comparator<String>() {
public int compare(String o1,String o2){
return (o1.substring(18,23)+o1.substring(0,1)).compareTo(o2.substring(18,23)+o2.substring(0,1));
}});
for (String line:linesAsList) System.out.println(line); // or whatever output stream you want
This phone's autocorrect is messing up my answer

Read the file into an ArrayList (instead of an array). Use the following methods:
// to declare the arraylist
ArrayList<String> lines = new ArrayList<String>();
// to add a new line to it (within your reading-lines loop)
lines.add(input.readLine());
Then, sort it using a custom Comparator:
Collections.sort(lines, new Comparator<String>() {
public int compare(String a, String b) {
String a5 = theFiveNumbersOf(a);
String b5 = theFiveNumbersOf(b);
int firstComparison = a5.compareTo(b5);
if (firstComparison != 0) { return firstComparison; }
String a1 = theDigitOf(a);
String b1 = theDigitOf(b);
return a1.compareTo(b1);
}
});
(It is unclear what 5 digits or what digit you want to compare; I've left them as functions for you to fill in).
Finally, write it to the output file:
BufferedWriter ow = new BufferedWriter(new FileOutputStream("filename.extension"));
for (String line : lines) {
ow.println(line);
}
ow.close();
(adding imports and try/catch as needed)

This code will sort a file based on mainframe sort parameters.
You pass 3 parameters to the main method of the Sort class.
The input file path.
The output file path.
The sort parameters in mainframe sort format. In your case, this string would be 19,5,CH,A,1,1,CH,A
This first class, the SortParameter class, holds instances of the sort parameters. There's one instance for every group of 4 parameters in the sort parameters string. This class is a basic getter / setter class, except for the getDifference method. The getDifference method brings some of the sort comparator code into the SortParameter class to simplify the comparator code in the Sort class.
public class SortParameter {
protected int fieldStartByte;
protected int fieldLength;
protected String fieldType;
protected String sortDirection;
public SortParameter(int fieldStartByte, int fieldLength, String fieldType,
String sortDirection) {
this.fieldStartByte = fieldStartByte;
this.fieldLength = fieldLength;
this.fieldType = fieldType;
this.sortDirection = sortDirection;
}
public int getFieldStartPosition() {
return fieldStartByte - 1;
}
public int getFieldEndPosition() {
return getFieldStartPosition() + fieldLength;
}
public String getFieldType() {
return fieldType;
}
public String getSortDirection() {
return sortDirection;
}
public int getDifference(String a, String b) {
int difference = 0;
if (getFieldType().equals("CH")) {
String as = a.substring(getFieldStartPosition(),
getFieldEndPosition());
String bs = b.substring(getFieldStartPosition(),
getFieldEndPosition());
difference = as.compareTo(bs);
if (getSortDirection().equals("D")) {
difference = -difference;
}
}
return difference;
}
}
The Sort class contains the code to read the input file, sort the input file, and write the output file. This class could probably use some more error checking.
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Sort implements Runnable {
protected List<String> lines;
protected String inputFilePath;
protected String outputFilePath;
protected String sortParameters;
public Sort(String inputFilePath, String outputFilePath,
String sortParameters) {
this.inputFilePath = inputFilePath;
this.outputFilePath = outputFilePath;
this.sortParameters = sortParameters;
}
#Override
public void run() {
List<SortParameter> parameters = parseParameters(sortParameters);
lines = read(inputFilePath);
lines = sort(lines, parameters);
write(outputFilePath, lines);
}
protected List<SortParameter> parseParameters(String sortParameters) {
List<SortParameter> parameters = new ArrayList<SortParameter>();
String[] field = sortParameters.split(",");
for (int i = 0; i < field.length; i += 4) {
SortParameter parameter = new SortParameter(
Integer.parseInt(field[i]), Integer.parseInt(field[i + 1]),
field[i + 2], field[i + 3]);
parameters.add(parameter);
}
return parameters;
}
protected List<String> sort(List<String> lines,
final List<SortParameter> parameters) {
Collections.sort(lines, new Comparator<String>() {
#Override
public int compare(String a, String b) {
for (SortParameter parameter : parameters) {
int difference = parameter.getDifference(a, b);
if (difference != 0) {
return difference;
}
}
return 0;
}
});
return lines;
}
protected List<String> read(String filePath) {
List<String> lines = new ArrayList<String>();
BufferedReader reader = null;
try {
String line;
reader = new BufferedReader(new FileReader(filePath));
while ((line = reader.readLine()) != null) {
lines.add(line);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return lines;
}
protected void write(String filePath, List<String> lines) {
BufferedWriter writer = null;
try {
writer = new BufferedWriter(new FileWriter(filePath));
for (String line : lines) {
writer.write(line);
writer.newLine();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (writer != null) {
writer.flush();
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
if (args.length < 3) {
System.err.println("The sort process requires 3 parameters.");
System.err.println(" 1. The input file path.");
System.err.println(" 2. The output file path.");
System.err.print (" 3. The sort parameters in mainframe ");
System.err.println("sort format. Example: 15,5,CH,A");
} else {
new Sort(args[0], args[1], args[2]).run();
}
}
}