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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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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Mar 1, 2014
One of the random number generators in Java extract the higher-order bits of the random number in order to get a longer period.
I'm not sure if I understand how this is done. Suppose that the random number r = 0000 1100 1000 1101. If we extract the 16 most significant bits from r; is the new number r = 0000 1100 or r = 0000 1100 0000 0000?
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Jan 26, 2014
Any link to the accurate explanation of binary trees in java?
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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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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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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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Apr 2, 2015
What static initialization blocks do in java?
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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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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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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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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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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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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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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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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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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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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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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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Feb 7, 2015
I am passing input from the user to a method that will initialize an array of the data (scores in this case). The method is filling the entire array with the last input value.
array initializer method
Java Code:
public static float[] inputAllScores(float validScore) {
float[] diverScores = new float[7];
for (int i = 0; i < diverScores.length; i++) {
diverScores[i] = validScore;
}
return diverScores;
} mh_sh_highlight_all('java');
[Code] .....
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Feb 14, 2015
I have an ArrayList of employee and ArrayLsit of bosses, and I want to keep those people in a temporary ArrayList , then ordain alphabetically by name, to sort I use the interface comparator.
The problem comes when I will order 2 ArrayList(workers and bosses), because every time I call I use these functions or not is ordered (sortByNameAlphabetical())
public class Employee {
private String name;
public String getName() {
return name;
}
@Override
public String toString() {
return name ;
[Code]...
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Jan 17, 2014
im new to java and i wanna make a program using java that can add order entries for a restaurant but how to... i was hoping something that would ask to person to input one or two items and before it calculates the total amount to be paid it will ask the guy who inputs the amount whether or not there are additional orders or not before it prints out the total amount... I am pretty sure it will need an if-else statement..
import javax.swing.*;
import java.util.Scanner;
public class OrderCalc {
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame aFrame = new JFrame("OrderCalc");
aFrame.setSize(500,250);
aFrame.setVisible(true);
[code]....
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Sep 22, 2014
I'm learning the swing options of Java, and my first exercise was the typical Chat Room. I got everything right: TextField, TextArea, the jpanel at left side and the buttons inside of it. BUT I can't order the 2 buttons (1 north, 1 south). I've already looked for answers, but didn't find anything and I tried to asked the teacher, but she was too lazy to look for the error. Here is my code:
f=new JFrame("Chat Room");
b1=new JButton("Send");
b2=new JButton("Emoticons");
public void showWindow(){
p1=new JPanel();
f.getContentPane().add(p1,BorderLayout.EAST);
p1.add(b1,BorderLayout.NORTH);
p1.add(b2,BorderLayout.SOUTH);
}
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Nov 20, 2014
I am unsure of something. In the following class, which is read first; the static field or the main method?
class Test{
static int a = 3;
public static void main(String args []) {
//some code}
}
I put some code in Eclipse and have tried to look at the hierarchy. It would point to all static fields being initialized in order from top to bottom, including the main method.I had thought that the main method was always the first thing in a public class to be initialized, regardless of where in the code it resides. Am I reading the Eclipse hierarchy wrong? I find Eclipse very difficult, especially since I typically code in Textmate. I just want to see how my code is operated upon,
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