User Event - Global Object Declaration
Mar 10, 2015
I have an application that uses an object that is declared globally for the class. Within a method that is triggered by a user event, it creates a new object and assigns it to this global object declaration. My question is, when the object is overwritten multiple times by the user selecting the button that calls this method, will the older instances be garbage collected or is there still a reference to them? Is there any downfall to this logic and if so what would be a solution.
View Replies
ADVERTISEMENT
Jul 27, 2013
Take this:
class test
{
static int i=j;
static int j=10;
.....
this will give illegal forward reference ....
but this will compile successfully ..
class test
{
static int i=test1();
static test1()
{
return 20;
}
}
.....
plz assume we have main method in both cases ..
java would be loading all static members first and would be assigning default values .. and then will be running all the initializers from to bottom ..Why second case is a compile success and not first .. as in second also test1 method is declared after its usage ..
View Replies
View Related
Feb 5, 2015
when a new object is created in Java it follows the idiom:
Object obj = new Object();
where the Object() constructor matches the object type Object.
But what if it doesn't? I understand from the Oracle Docs on creating objects and polymorphism that the constructor must be in that object's class or one of its subclasses. However, suppose we wanted to declare a new stack. My first instinct would be:
Stack s1 = new Stack();
But I assume it's valid to do it this way, too:
Object s2 = new Stack(); // Is there a difference here? What are we really saying about s2? I'm guessing s2 is simply an empty stack, but only has access to the Object class methods? I'm not sure why someone would ever do this, but I want to solidify my understanding of the Java hierarchy. Are there really any circumstances where someone would use a subclass's constructor when creating a new object?
View Replies
View Related
Feb 28, 2015
java.awt.Component is an abstract class, and it's direct Sub-classes are Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, Text Component
So, when I use addXListener(mylistenerclass m);//which is a method of Component class which object is holding the list of all listeners, for a particular Event Source?
I am under the assumption that - there is an Event Source Object(possibly static) for every Event Source type(mouse, keyboard etc) that holds a list of destinations(classes that implements their listener interface) - added to the the object via addXListener method. When an event happens(mouse click, drag etc) the Event Source Object creates an Event Object and send it to all the destinations. Is my assumption correct? I can't seem to find the location or declaration of Event Source Object and the list where it stores it's registered destinations.
View Replies
View Related
Jun 18, 2014
We are doing a Timeline project, So this is what i want to do:
Pressing a "New Event" button opens the New event window where you are supposed to write input in three fields, name, date, and information. There is also a button "Create" that when i press that button, i want to take all the input from the fields and save/send it to our database, and go back to the timeline GUI. With this, i want a new event object to be created(in this case i have done several shapes in a group) so basically a new group i want to be added. All the information is suppose to be taken from the database right after i create it.
I'm pretty stuck on how i should solve this, for the moment have a group called event that i add on the canvas. First thing that pops up in my head is a void method that draws the event, or maybe a temporary array.. P
package application;
import controllers.CreateEventController;
import application.EventPop;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Cursor;
[Code] ....
View Replies
View Related
Sep 22, 2014
I’m teaching myself Java. I am a fairly proficient programmer in other languages, but this is the first OO language I’m doing.I have a question that is a bit hard to summarize. Or it should be: how can I pass on an object (or variable) to an event listener?
I am writing an application in which you can play a Sudoku game. I have separated the “logic” or the “model”(the classes with Sudoku data structures and methods to manipulate them) from the presentation (the view and the controller).The main method starts off as follows:
SudokuModel model = new SudokuModel();
SudokuView viewController = new SudokuViewController(model);
The first line creates class for the logic and the second line creates the class for the view and the controller. Since the view and the controller need access to the business logic, the model is passed on to the ViewController class.The SudokuViewController class creates the user interface in Swing and it handles the user input. For the user input I have created a number of listeners, like this:
table.addKeyListener(this);
Now these listeners need access to the model since they update it. However, as far as I’m aware the only parameter passed on to an event listener is the event itself. So these event listeners do not have direct access to the model, even though it is passed on to the constructor of the class SudokuViewController.
To circumvent this, I made model2 an attribute (variable) of the class SudokuViewController. The constructor of the class sets this variable as follows:
model2 = model;
Now the event listeners have access to model2, which they can manipulate.This works. However, I think it is an ugly solution, introducing an additional object (model2). I’d like to pass on the object named model to the event listener, but this doesn’t seem to be possible.
View Replies
View Related
Oct 7, 2014
I am new to Java and have read books, the Java docs, and searched the Internet for my problem to no avail. I have an Array of objects that contains strings. How can I get the object's strings to print in a list so that the user can select that object to manipulate its attributes? For example, the user can select "Guitar 1" from a list and manipulate its attributes like tuning it, playing it, etc. I have a class called Instruments and created 10 guitar objects.Here is the code:
Instrument [] guitar = new Instrument[10];
for (int i = 0; i < 10; i++) {
guitar[0] = new Instrument("Guitar 1");
guitar[1] = new Instrument("Guitar 2");
guitar[2] = new Instrument("Guitar 3");
guitar[3] = new Instrument("Guitar 4");
guitar[4] = new Instrument("Guitar 5");
guitar[5] = new Instrument("Guitar 6");
[code]...
View Replies
View Related
Jun 29, 2014
How to use common functions and constants in one jsp page which are used in another jsp page on page load time?
View Replies
View Related
Aug 22, 2014
Is there a way to have global variable in Java associated to a process ?
I'm coming from PL/SQL world, I'm looking for something like package variables.
View Replies
View Related
Aug 16, 2013
I am very much new to jsp and servlet. I want to set global error page for every exception occured at server side. I am trying with following code , but something is going wrong and I am not able to c error page.
package com.web;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
[Code] ....
View Replies
View Related
Jun 13, 2014
The method below is called within a large loop in another method. The code has been boiled down to easily show the problem I'm having. I found that the method worked fine (prompts user for input, gets input, returns input) until I added a statement at the end of the method that closes the Scanner object. When the kb.close() statement is present, the method works the first time through, but subsequent calls to this method only display the prompt and the Scanner object never waits for the user to input anything thereafter.
public int scanIt()
{
int i;
Scanner kb = new Scanner(System.out);
System.out.print("==> "); // prompt for input
if(kb.hasNextInt())
{
i = kb.nextInt();
System.out.println("User entered " + i);
}
kb.close();
}
View Replies
View Related
Feb 17, 2015
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class App {
public static void main(String[] args) throws IOException {
Scanner keyboard = new Scanner(System.in);
System.out.println("Please Select an option > ");
[Code] .....
View Replies
View Related
Oct 26, 2014
Netbeans tells me it's an illegal start of expression during the initialisation of the interactWithUser method.
public class InvertLetter {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
/**
* String mit den Kleinbuchstaben.
*/
final String lowercase = "abcdefghijklmnopqrstuvwxyz";
[Code] ....
View Replies
View Related
Apr 9, 2015
Let's say within a class I create a method that takes care of creating a java swing layout with labels, buttons etc.. then attach an action listener (inner class) for each button to change a respective label text. All I would need is that the action listener method can access and modify the label as needed.
Have read about static, protected, private, getters and setters but honestly bit confused about which structure should be adopted as a best practice. Global static protected variables for the labels along with private inner classes implementing ActionListeners believe will do the trick and will be able to access the labels but not convinced this is good practice.
View Replies
View Related
Apr 30, 2015
My Question is Suppose I am declaring an String array as
String[] a
or
String a[]
or
Comparable[] a
Will there be any performance or other advantage or disadvantage using these syntax?
View Replies
View Related
Feb 26, 2015
import java.util.HashSet;
import java.util.ArrayList;
public class Graph
{
double [] [] adj;
graph (double [] [] a)
{
adj= new double [a.length][a.length];
for (int i=0;i<a.length;i++)
for (int j=0;j<a.length;j++)
adj[i][j]=a[i][j];
}
C:UserscDesktopGraph.java:: error: invalid method declaration; return type required
graph (double [] [] a)
View Replies
View Related
Oct 6, 2014
I have an Array of objects that contains strings. I am new to Java and have read books, the Java docs, and searched the Internet for my problem to no avail. How can I get my strings to print in a list so that the user can select an object to manipulate its attributes? I have a class called Instruments and created 10 guitar objects. Here is the code:
Instrument [] guitar = new Instrument[10];
for (int i = 0; i < 10; i++) {
guitar[0] = new Instrument("Guitar 1");
guitar[1] = new Instrument("Guitar 2");
guitar[2] = new Instrument("Guitar 3");
guitar[3] = new Instrument("Guitar 4");
[Code] ....
View Replies
View Related
Feb 13, 2014
I tried this:
String[][]f = new String[1][1] {{"Harry"}{"Hairy"}};
I also tried this:
String[][]f = new String[1][1] {{"Harry"},{"Hairy"}};
but I get an error
View Replies
View Related
Apr 13, 2014
Ok say you have
public class MyClass {
private int x = 5;
Object myObject = new Object();
public MyClass(){
}
}
When would the myObject be created? Before or after the constructor? And does this mean you can't pass
this into the parameters of that object?
View Replies
View Related
Feb 27, 2014
I'm new to Java and have been stuck on how to use a final declaration statement once it's made. Below is a class I'm creating with the intention of calling it under a main method. I don't understand if I'm supposed to do anything else, like do some sort of get/set, or if the final static line is all I need. And, I don't know how I call it to the main method once I do.
public class Shirt//class name.
{
int collarSize;//data field.
int sleeveLength;//data field.
public final static String MATERIAL = "cotton";//final data field for material.
[Code] ....
View Replies
View Related
Dec 23, 2014
I started learning JSTL (Java Standard Tag Library) and i got to know that i need to mention this directive in JSP page
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
in order to use JSTL tags.
I am not able to understand what does this URI exists at all ?? I feel it making things complex and meaningless or else i am missing something hidden and secret.
View Replies
View Related
May 17, 2015
Whilst pre-preparing for java certification, one of the online mock exams has slightly confused me by saying my answer was incorrect for multi-dimension array 'declaration and instantiation'.
This is one of the answers i chose - which was marked as incorrect
a)
int[][] array2d = {{123}, {4,5}};
Which looks absolutely fine to me.One of the other answers, which i agree is correct and so does the mock exam is
b)
int [][] array2d = new int[2][2];
View Replies
View Related
Sep 3, 2014
I have one interface with three(more than one) method declaration. In the subclass that implements it I want to define only one method not all three not even blank definition of them.Is there any keyword or method for that. How to do it? Is it possible to do it? In GUI we use adapter classes to achieve it. What for console application?
View Replies
View Related
Jan 30, 2014
I have doubts in string declaration. As I know we can declare string in two ways:
1. String a=new String("Hello");
2. String b="Hello";
What is exact difference between them? Another thing is when I check (a==b) it retuns me false, but when I check a.equals(b) it returns me with true. Why So?
View Replies
View Related
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?
View Replies
View Related
Jun 3, 2014
I have to implement all the stack methods in java such as push, pop empty, not using the ready methods but have to create them and to execute an exercise but is sth wrong with it
public class Stiva {
/** the problem is here how to declare the stack 1 and stack 2 and kreu(head) gjmax(size)*/
int Gjmax;
int array[] = new int[Gjmax];
int kreu;
private Stiva stiva1;
private Stiva stiva2;
[Code] .....
View Replies
View Related
