Develop Reference

When should i create inner class or inner static class?

I am aware about the static keyword, but in short. My attempt is to create inner static class since it's related to outer class. The practical problem is I am confused how to access it. My reason use static class is that I just need one instance of it per application?
Please correct if you found any misconseption, and give real usage of the class / static class.
public class DbPredecessorTest {
List<Book> db;
Book book;
Integer numberOfBooks;
static BufferedReader reader;
static {
try {
reader = new BufferedReader(new FileReader(Main.fileLoc));
} catch (FileNotFoundException e) {
throw new RuntimeException(e);
}
}
static class Helper {
DbPredecessor dbPredecessor= new DbPredecessor();
Long getLines() {
return reader.lines().count();
}
}
My directionless attempt:
class SomeTest {
#Test
void ableToSave() throws IOException {
db.add(book);
boolean save = Helper.dbPredecessor.save(db);
assertEquals(true, save);
}
#Test
void save_should_increaseLine() throws IOException {
db.add(book);
// numberOfBooks= (int) Helper.get
boolean save = dbPredecessor.save(db);
assertEquals(numberOfBooks+1, reader.lines().count());
}
}

That's not the reason to use a static inner class. A static inner class is functionally an ordinary Java class, the only real reason you would have one is to indicate it's related to the outer class in some way or to make it private.
You could just use a normal static method here:
public class DbPredecessorTest {
static long getLines() {
return reader.lines().count();
}
}
and then use it like so:
long numberOfBooks = DbPredecessorTest.getLines();

java Object null after instance and calling inside method

can anyone help me with this issue, i'm working with java using SQLMap(ibatis).
i have 3 class which is MainConfiguration, SQLMap, DBUtility.
Main Configuration (this class is using to set an object inside SQLMap class)
public class MainConfiguration
{
public static String file = "configuration/db/SQLMapConfig.conf";
public static void main(String[] args) throws Exception
{
new MainConfiguration().loadConfiguration();
}
public static void loadConfiguration()
{
SQLMap.setMapFile(file);
List list = DBUtility.loadUsers();
}
}
SQL Map (this class is the getter and setter of and object)
public final class SQLMap
{
private static SqlMapClient sqlMap;
public static void setMapFile(String sMapFile)
{
try
{
sqlMap = SqlMapClientBuilder.buildSqlMapClient(new FileReader(sMapFile));
}
catch (Exception e)
{
throw new RuntimeException("Error initializing SqlMapClient class", e);
}
}
public static SqlMapClient getSqlMapInstance()
{
return sqlMap;
}
}
DBUtility (this class is where object instance and get object from SQLMap class)
public class DBUtility
{
// object utility
protected static SqlMapClient sqlMap = SQLMap.getSqlMapInstance();
//constructor
public DBUtility() throws Exception
{
}
public static List loadUsers()
{
//it's working
logger.info("SQLMap Get Instance = " + SQLMap.getSqlMapInstance());
//it's not working
logger.info("SQLMap Get Instance = " + sqlMap);
//code below will be error because of null sqlMap
try
{
listUser = sqlMap.queryForList("getUsers");
}
catch (Exception sqle)
{
logger.error("Error on load all user", sqle);
}
return listUser;
}
}
the logger give me this :
SQLMap Get Instance = com.ibatis.sqlmap.engine.impl.SqlMapClientImpl#76707e36
SQLMap Get Instance = null
how come the second log give me null, even i have instance the object?

Your field sqlMap is initialized when the DBUtility class is loaded, which apparently happens before SQLMap.setMapFile(file); is called. So, sqlMap points at different things: null in the static field, and an actual instance when you call the getter in loadUsers().
The problem is that DBUtility looks up the sqlMap too early. It has to wait until the file is passed to SQLMap. Change your code like this to delay the initialization of DbUtility.sqlMap:
public static void loadConfiguration()
{
SQLMap.setMapFile(file);
DBUtility.initMapClient(); // notify DBUtility
List list = DBUtility.loadUsers();
}
public class DBUtility
{
protected static SqlMapClient sqlMap; // do not initialize too early
public static void initMapClient()
{
sqlMap = SQLMap.getSqlMapInstance(); // wait for SQLMap to be ready
}
Of course, it would be simpler if you did not even have the sqlMap field in DBUtility. Just call SQLMap.getSqlMapInstance() every time you need it. This is especially important in case the instance ever changes:
listUser = SQLMap.getSqlMapInstance().queryForList("getUsers");
Read When are static variables are initialized? for a more detailed explanation of static fields.

Xpages: How to ensure my cacheBean only loads once

Still struggling with properly making a cacheBean. I think I want the bean to be a singleton, from what I have read. Will only need
one instance of it. Use it to get often used keywords and so on.
http://blog.defrog.nl/2013/02/prefered-way-for-referencing-beans-from.html
I used this pattern to make my CacheBean (and used a utility method).
If I make this a managedBean by putting it into Faces-config, then I can easily get the value of models
<xp:text escape="true" id="computedField1"
value="#{CacheBean.models}"></xp:text>
The JSF takes care of instantiating the bean for me.
But I don't want it to reload the same values (like models) over and over. I thought that to get that to happen I needed to make
a POJO and grab the currentInstance of the bean, as in the url.
However, when I made this change (taking the bean out of the faces-config file, I cannot seem to get a handle on the properties.
This won't even compile:
<xp:text escape="true" id="computedField1"
value="#{Cache.getCurrentInstance().models}">
</xp:text>
What am I doing wrong?
================================
package com.scoular.cache;
import java.io.Serializable;
import org.openntf.domino.xsp.XspOpenLogUtil;
import com.scoular.Utils;
public class CacheBean implements Serializable {
private static final long serialVersionUID = -2665922853615670023L;
public static final String BEAN_NAME = "CacheBean";
private String pcDataDBpath;
private Vector<Object> models = new Vector<Object>();
public CacheBean() {
initConfigData();
}
private void initConfigData() {
try {
loadModels();
loadDBPaths();
} catch (Exception e) {
XspOpenLogUtil.logError(e);
}
}
// Getters and Setters
public static CacheBean getInstance(String beanName) {
return (CacheBean) Utils.getVariableValue(beanName);
}
public static CacheBean getInstance() {
return getInstance(BEAN_NAME);
}
public String getPcDataDBpath() {
return pcDataDBpath;
}
public void setPcDataDBpath(String pcDataDBpath) {
this.pcDataDBpath = pcDataDBpath;
}
public void loadDBPaths() {
Session session = Factory.getSession();
Database tmpDB = session.getCurrentDatabase();
pcAppDBpath = (tmpDB.getServer() + "!!" + "scoApps\\PC\\PCApp.nsf");
pcDataDBpath = (tmpDB.getServer() + "!!" + "scoApps\\PC\\PCData.nsf");
compDirDBpath = (tmpDB.getServer() + "!!" + "compdir.nsf");
}
public void loadModels() {
try {
Session session = Factory.getSession();
Database tmpDB = session.getCurrentDatabase();
Database PCDataDB = session.getDatabase(tmpDB.getServer(), "scoApps\\PC\\PCData.nsf");
ViewNavigator vn = PCDataDB.getView("dbLookupModels").createViewNav();
ViewEntry entry = vn.getFirst();
while (entry != null) {
Vector<Object> thisCat = entry.getColumnValues();
if (entry.isCategory()) {
String thisCatString = thisCat.elementAt(0).toString();
models.addElement(thisCatString);
}
entry = vn.getNextCategory();
}
} catch (Exception e) {
XspOpenLogUtil.logError(e);
}
}
p
ackage com.scoular;
import javax.faces.context.FacesContext;
public class Utils {
public static Object getVariableValue(String varName) {
FacesContext context = FacesContext.getCurrentInstance();
return context.getApplication().getVariableResolver().resolveVariable(context, varName);
}
}

When the bean has the right scope you can access the bean directly if is created.
private static final String BEAN_NAME = "CacheBean";
//access to the bean
public static CacheBean get() {
return (CacheBean) JSFUtil.resolveVariable(BEAN_NAME);
}
//in my JSFUtil class I have the method
public static Object resolveVariable(String variable) {
return FacesContext.getCurrentInstance().getApplication().getVariableResolver().resolveVariable(FacesContext.getCurrentInstance(), variable);
}
so in a Java Class you can call
CacheBean.get().models
in EL you can use
CacheBean.models

I can tell you why it's not compiling at least.
value="#{Cache.getCurrentInstance().models}"
That's EL. So there should not be a get or a (). You want
value="#{Cache.currentInstance.models}"
And check your var name as I thought you were using CacheBean and not Cache.

Java: message system needs to be able to pass various objects

I'm writing a messaging system to queue actions for my program to execute. I need to be able to pass various objects by the messages. I currently have a Msg object that accepts (Action enum, Data<?>...object). The Data object is intended to be a wrapper for any object I might pass.
Currently the Data object uses this code, with generics:
public class Data<T> {
private T data;
public Data(T data){
this.data = data;
}
public T getData(){
return data;
}
}
The Msg object takes Data<?>... type, so Msg has a Data<?>[] field.
If getData() is called on a Data<?> object, it returns the Object type. Obviously not ideal.
I need to be able to pass, say, Image objects as well as String objects. I'm certain there's a better way of passing arbitrary data.

The reason you're having trouble is that you're trying to get the static typing system of Java to do something that it can't. Once you convert from a Data<T> to a Data<?>, whatever T was is effectively lost. There's no clean way to get it back.
The quickest way to get it to work (from what you have right now) is to start throwing casts everywhere, like this:
Data<?> d = new Data("Hello");
String contents = (String)d.getData();
This is kind of a terrible idea, so let's go back to the drawing board.
If (ideally), you have all of the types you could ever need ahead of time (i.e. every Data is either a String or an Image or an Integer), then you can pretty easily (though it's a bit tedious) define a Sum type (aka a union if you're coming from C) of the different types of data you'll have to handle. As a class invariant, we assume that exactly one of the fields is non-null, and the rest are null. For this example I'll assume it can be either a String, an Image, or an Integer, but it's fairly simple to add or remove types from Data as necessary.
public class Data {
private Image imgData;
private String stringData;
private Integer intData;
public Data(Image img) {
this.imgData = img;
}
public Data(String stringData) {
this.stringData = stringData;
}
public Data(Integer intData) {
this.intData = intData;
}
public boolean isImage() {
return imageData != null;
}
public boolean isInteger() {
return intData != null;
}
public boolean isString() {
return stringData != null;
}
public Image asImage() {
if(! isImage()) throw new RuntimeException();
return imgData;
}
public Image asString() {
if(! isString()) throw new RuntimeException();
return stringData;
}
public Image asInt() {
if(! isInt()) throw new RuntimeException();
return intData;
}
}
One necessary side effect is that we cannot wrap null without causing exceptional behavior. Is this is desired, it isn't too difficult to modify the class to allow for it.
With this Data class, it's pretty easy to do if-else logic to parse it.
Data d = ....... //Get a data from somewhere
if(d.isImage()) {
Image img = d.asImage();
//...
} else if (d.isString()) {
String string = d.asString();
//...
} else if (d.isInteger()) {
Integer i = d.asInt();
//...
} else {
throw new RuntimeException("Illegal data " + d + " received");
}

If you call getData().getClass() you will get the class or type that was passed, which doesn't seem to me to be the same as an Object. You might not know what you are getting, but you can either find out or define a common interface for everything you might pass. You could for example, call toString() or getClass() on anything passed. Your question is that you are passing any conceivable object, so my question is what are you going to do with it? If you are going to serialize it into a database you don't need know anything about what type it is, otherwise you can test it or call a common interface.
public class PlayData {
class Msg {
private List<Data<?>> message = new ArrayList<Data<?>>();
public void addData(Data<?> datum) { message.add(datum); }
public void printTypes() { for ( Data<?> datum: message ) { System.out.println(datum.getData().getClass()); } }
}
class Data<T> {
private T value;
public Data(T value) { this.value = value; }
public T getData() { return value; }
}
class Listener {
public void receive(Msg msg) { msg.printTypes(); }
}
class Sender {
private Listener listener;
public Sender(Listener listener) { this.listener = listener; }
public void send(Msg msg) { listener.receive(msg); }
}
class MyPacket {
int i;
public MyPacket(int i) { this.i = i; }
}
public static void main(String[] args) throws Exception { new PlayData().run(); }
public void run() throws Exception {
Sender sender = new Sender(new Listener());
Msg msg = new Msg();
msg.addData(new Data<String>("testing") );
msg.addData(new Data<MyPacket>(new MyPacket(42)) );
sender.send(msg);
}
}

Mocking a DAO in Mockito

I'm just getting into testing of code. I have done unit tests before but haven't really isolated them. So they were more like integration test (indirectly). I want to give Mockito a try and I have added it to my Intellij IDE.
But I have no idea of how to actually implement mocking at all. There are examples on their website but I just can't wrap my head around the concept of mocking. I know that one uses mocking to isolate the unit testing to ensure that the errors are in the unit itself and not in a dependency.
I wrote the following:
#Test
public void testChangeMemberReturnsTrue() throws Exception {
Member tempMem = new Member();
tempMem.setMemberFirstName("Swagrid");
tempMem.setMemberLastName("McLovin");
tempMem.setMemberID("SM666");
SQLDUMMY.saveMember(tempMem); //Save member to dummy DB.
Member checkMem = new Member();
ArrayList<Member> memArr = SQLDUMMY.getAllMembers();
for (Member m : memArr) { // Look through all saved members
if (m.equals(tempMem)) { // If match, save to checkMem
checkMem = m;
}
}
assertTrue(tempMem.equals(checkMem)); // Make sure they are really equal.
String newfirstname = "Darius";
String newlastname = "DunkMaster";
assertTrue(memhandling.changeMember(tempMem, newfirstname, newlastname));
}
And here is the actual method:
public boolean changeMember(Member mem, String n1, String n2) {
try {
ArrayList<Member> memArr = SQLDUMMY.getAllMembers();
for (Member m : memArr) {
if (m.equals(mem)) {
m.setMemberFirstName(n1);
m.setMemberLastName(n2);
m.setMemberID(ensureUniqueID(m, m.getMemberID())); //Just a method call to another method in the same class to ensure ID uniqueness.
return true;
}
else {
return false;
}
}
}
catch (Exception e) {
System.out.println("Error4.");
}
return false;
}
I'd like to mock the SQLDUMMY (Which I created just to see if my tests would pass at all, which they do.) The SQLDUMMY class looks like this:
public class SQLDUMMY {
private static ArrayList<Member> memberList = new ArrayList<>();
private static ArrayList<Ship> shipList = new ArrayList<>();
public static ArrayList<Member> getAllMembers() {
return memberList;
}
public static void saveMember(Member m) {
memberList.add(m);
}
public static void deleteMember(Member memIn) {
memberList.remove(memIn);
}
public static void saveShip(Ship newShip) {
shipList.add(newShip);
}
public static ArrayList<Ship> getAllShips() {
return shipList;
}
public static void deleteShip(Ship s) {
shipList.remove(s);
}
}
It basically just consists of getters and add/remove for the ArrayLists that act as a contemporary DB storage.
Summary: How can I mock the SQLDUMMY class (DAO), so it is no longer a dependency for the Unit tests?

You need to read on how Mockito works.
The basic idea is that it extends you class and and overrides all methods and allows you to return what ever you want it too.
Syntax is :
SQLDummy sqlDummy = Mockito.mock(SQLDummy.class);
Mockito.when(sqlDummy.getAllShips()).thenReturn(new ArrayList< Ship >())