Will Initialization Of HashMap On Different Place Make Any Difference

Nov 21, 2014

public class HashMapTest {
private static HashMap mp;
public static void main(String[] args) {
// TODO Auto-generated method stub
mp=new HashMap<String, String>();
}
}

This is My Code if I create Object in two place
1)Outside main() method but within class.
2)Inside main() method like above

Will these two approach makes any difference ?

I am asking a general senerio for creating any Type of Objects Primitives or References?

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Difference Between Explicit In Class Initialization And Non Static Instance Initialization

Dec 20, 2014

I come from a C++ background and I recently started learning Java from "Thinking in Java" 4th Edition by Bruce Eckel.What's the difference between:

// explicit in class initialization
// saw this on page 126

class A {

}

public class B {
A obj1 = new A();
A obj2 = new A();
}

and

// non static instance initialization
// saw this on page 132

class A {
}
public class B {
A obj1;
A obj2;
{
obj1 = new A();
obj2 = new A();
}
}

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Jul 10, 2014

What are the difference between hashmap, linkedlist and arraylist ... when they are used and why?

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I want to know if there is any general rule/pattern about things which give compilation fails and things which go for Runtime error/exception. OR only way is to remember all of them and there is no actual pattern in it.

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Apr 29, 2014

I am trying to make a game, for some reason i have begun to get a java.lang.StackOverflowError.

I am not exactly sure how i can fix it. only removing line 14 from infopannel1 (and everything that used that class.) seems to work. im not sure what else i can do to fix it. or why its resulting in stack overflow for that matter.

I am putting in a link for the files i wrote this using bluej (several classes have no relevance, errorv2, demonstration, folderreadertest, ReadWithScanner, saveloadtest, menutest,rannum, and menutestTester. are all irrelivent to my problem.)

[URL] .....

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Order Of Initialization

Sep 17, 2014

I came across this code which proves that variable initialisation occurs before even constructors are called.However, I am confused over some things.

Firstly, from my understanding, when a new House object is created in this line House h = new House(); , the no-arg constructor of the House class is called.

Since the no-arg constructor House() is called, why are all the creation of Window objects being run first ? Shouldn't Java jump straight into the no-arg constructor House() ?

class Window {
Window(int marker) { System.out.println("Window(" + marker + ")"); }
}
class House {
Window w1 = new Window(1); // Before constructor
House() {
// Show that we’re in the constructor:
System.out.println("House()");
w3 = new Window(33); // Reinitialize w3

[code]...

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JSF :: UI Layout Initialization Error

May 12, 2014

I am using netbeans 7.2, glassfish 3.1.2, JSF 2.1 and Primefaces 3.2. When I add more than three menu tabs, I get this error ui layout initialization error the center-pane element does not exist the center-pane is a required element. This is my template.xhtml code:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:p="http://primefaces.org/ui">

[Code] ....

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Error In Array Initialization?

Sep 9, 2014

public class SavingsAccount extends Account {
private static final double MIN_BALANCE = 100.00;
private static final double RATE = 0.035;
public SavingsAccount(Customer customer, double bal, String accountNum,
Transaction[] trans) {
super(customer, bal, accountNum, trans);

[code]....

When I execute this code there is an error in Transaction array initialization. Change the Saving account constructor from (String customer,double balance, String accountnumber,Transaction[] tr) to (String customer,double balance, String accountnumber,Transaction tr)

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What Are Static Initialization Blocks

Apr 2, 2015

What static initialization blocks do in java?

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Initialization And Default Values

Mar 20, 2015

I have a question related to q44 of Examlab.

public static void main(String... args) {
String i;
// String i = null; that would compile
if (i == null) {// this line does not compile as i was not initialized
System.out.print("A");
} else {
System.out.print("B");
i = "A";
main("A", "B");
}
}

Why does the above code not compile although the statement String i should lead to an initialisation of i to the value of null which is the default value for Strings.

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Default Initialization To Appropriate Value By Compiler

Feb 20, 2014

I remember reading Instance variables & local variables (in methods) are initialized to appropriate value by the compiler.

Is this true for static class variables and variables in nested classes ?

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JSP :: Accessing ServletConfig Initialization Parameters

May 12, 2014

I am trying a simple program to access ServletConfig initialization parameter in a jsp. But I am not clear how its working. This is web.xml

<web-app>
<servlet>
<servlet-name>Myservlet</servlet-name>
<jsp-file>/JjspInit.jsp</jsp-file>
<init-param>
<param-name>para</param-name>
<param-value>valu</param-value>

[Code] ....

Now If I hit /Allen it sets init parameter for both servlet MyServlet and jsp JjspInit. I don`t have any servlet all I have is a web.xml and a jsp page. But accessing JjspInit.jsp directly gives null.

How hiting the url /Allen prints valu. This code is on JjspInit.jsp .

So does that mean that in web.xml I have registered this jsp as the target for /Allen. And one more question directly accessing the jsp page shows null it means init parameter haven`t been set.

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Dynamic Initialization Of 2D Array Of Objects?

Aug 15, 2014

if, instead of an ArrayList, can I do the following to initialize a Dyanmic array ? :

First, in my class, I have :

class Example{
private int rows;
private int columns;
private AnotherClass[][] 2DArray;
public Example(int rows, int columns){
this.rows = rows;
this.columns = columns;

[code]....

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Servlets :: Initialization With Different Scope / Context

Jan 13, 2015

I want to initialize my servlet based on the scope of my application.

For example, I have multiple admins with their respective email address.

I want to perform action within my servlet based on the given environment.

Would this be the right approach, if I set the admin email addresses in my web.xml as init-param:

<servlet>
<servlet-name>ServletName</servlet-name>
<servlet-class>com.mkyong.ServletDemo</servlet-class>
<init-param>
<param-name>admin1</param-name>

[Code] .....

Now if I am in the admin 1 environment, I would initialize my servlet with request parameter admin=1 and the servlet should load email address of admin 1 and similarly when in the environment 2, should load the servlet with admin 2.

call environment 1:
/servlet/Demo?admin=1
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException{

[Code] .....

I could do the same by putting the email address of the respective admin as request param value, but i don't want to the email address to appear in the url.

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Initialization Of Variables At Class Level

Feb 11, 2014

if I declare

class Example
{
int x=10;
......
}

It is not showing any error but when I declare

class Example
{
int x;
x=10;
............
}

it showing compile time error ....

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Why Array Initialization Does Not Give Error

Feb 18, 2014

int[][] array1 = {{1, 2, 3}, {}, {1, 2,3, 4, 5}};

it initializes 3 one dimentional array:

1 - {1, 2, 3}
2 - {}
3 - {1, 2,3, 4, 5}

but it only declares two dimensional arrays.

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Final Field Initialization With Exceptions

May 11, 2014

consider:
 
class A {
     final Object b;
     public A(C c) {
          try {
               b = c.someMethodThatMayThrowSomeException();
          } catch (SomeException e) {
               b = null; // This line results in compiler error: "variable b might already have been assigned"
          }
     } // take away b=null line and you get "variable b might not have been initialized" on this line
}
 
Why? How could 'b' be assigned if the exception was thrown?
 
Btw, the workaround is to wrap the method call:
 
private final Object initB() {
     try {
          return c.someMethodThatMayThrowSomeException();
     } catch (SomeException e) {
          return null;
     }
}
 
and use b = initB(); in the constructor.  But that seems like it should be unnecessary.

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Jan 29, 2015

I know that I can declare and initialize an member variable inside a class in a single statement but I can't do them on separate sentence. Why?

For example, I am allowed to do the following,

class A{
int a = 5;
// rest of the class
}

But I am not allowed to do this,
class A{
int a;
a = 5; // it doesn't compile even when the variable 'a' is static
// rest of the class
}

Why java don't allow me to do that?

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String Initialization - Given 3 Names Say Which Oldest And Which Youngest

Jan 14, 2015

/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package vecchiogiovane;
import java.io.*;
public class Vecchiogiovane {
  /**
* @param args the command line arguments
*/
public static void main(String[] args) throws Exception{
 
[Code] .....

run:

run:

ins first name:
aldo
ins first age:
35
ins second name:

[Code] ....

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Apr 21, 2015

/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/

package BaiVeNha;
import java.util.ArrayList;
import java.util.List;
import javax.swing.table.DefaultTableModel;

[Code] ....

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May 21, 2014

I've been trying to finish this blackjack program I have been making for my programming class, however, there are a few bugs I can't seem to iron out. It's a pretty short program, it's just that I'm an idiot and can't figure basic stuff like this out. Specifically, when I try and run it, I get this error:

Error occurred during initialization of VM
java.lang.OutOfMemoryError: unable to create new native thread

Java Code:

import static java.lang.System.*;
import java.applet.Applet;
import java.util.Scanner;
import java.io.*;
import java.util.Random;
import java.util.Date;

[Code] .....

So, obviously I'm doing something horribly wrong.

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How To Keep Character In Place With Up And Down To Move

Jan 30, 2014

I noticed it is a huge success to have the backgrounds of games move and the character just move up and down and dodge obstacles.How Do I make a background that scrolls horizontally to the left? I know how to keep the character in place with up and down to move, but not sure how to go about making the background move with obstacles.

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How To Use Events In Place Of For Loop

Jun 30, 2014

I have two questions:

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if (player.getLocation().getX() == 10) {
}
}

I'm not sure as to how to use Events in place of a for loop. I've been thinking on this for days, but I'm still stuck. Any example of using an Event instead of a for loop?

2. Is there any way to accept multiple connections on a server without using a while loop? Maybe use Events to handle the acceptance of connections?

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Jun 6, 2014

Is it possible to enable & disable "jdk.certpath.disabledAlgorithms" property programmatically. I want to remove all disabled Algorithms for some time and later I will enable it.

Or is it possible to enable only for a particular place & not in a JVM level. I want that Algorithm need to be enabled for a piece of code, but I don't want it to the remaining part of the application.

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Feb 17, 2014

I am making a Dice Roll GUI and I have most of it down and I only need this constructor to work for the program to work (I think). I don't know where to place the constructor, I tried placing it around the RollButton class but it still didn't work and gave me java error constructor in class cannot be applied to given types

Here's my constructor:

private JPanel panel;
public RollButton(JPanel panel){
this.panel = panel;
}

Here's my code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.util.Random;
import javax.imageio.ImageIO;

[code]....

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