creating a window in java

lemon09 · 10-01-2009, 04:24 AM

hello friends,

i want to create a window in java using java.awt.Window.

i tried out the following code:

Code:

import java.awt.*;

public class TestWindow
{
       public static void main(String []args)
       {
	      new CreateWindow();
       }
}

public class CreateWindow extends Window
{
       CreateWindow()
       {
	      //create an instance of Window
	      //the following statement creates an invisible window 
	      Window win = new Window(Window owner);
	      //next we make the window visible.
	      win.setVisible(1);
       }
}

and i got the following error during compilation:

Code:

$ javac TestWindow.java
TestWindow.java:20: ')' expected
              Window win = new Window(Window owner);
                                            ^
TestWindow.java:20: illegal start of expression
              Window win = new Window(Window owner);
                                                  ^
2 errors

can anybody please correct me...........

gr33d · 10-01-2009, 04:38 AM

are you trying to cast the owner object to type Window?

i'm not intimately familiar with awt (i use swing) but the line:
Window win = new Window(Window owner);

should be
Window win = new Window(owner);

lemon09 · 10-01-2009, 04:41 AM

actually i got that code from the java docs itself...so i just gave it a shot.

gzunk · 10-01-2009, 04:47 AM

A few things wrong with your code. Here's a fixed version

Code:

import java.awt.*;

public class TestWindow
{
       public static void main(String []args)
       {
	      CreateWindow();
       }
       
       public static void CreateWindow()
       {
	      //create an instance of Window
	      //the following statement creates an invisible window 
	      Window win = new Window(null);
	      
	      win.setSize(300,200);

	      //next we make the window visible.
	      win.setVisible(true);
       }
}

First of all, you wouldn't (normally) create two classes in the same file. You can, but it's not normally done. I've changed your second class to be a method on your first class.

Secondly, the constructor to Window should be passed null if you don't want it to have an owner. And if you want to pass in a variable you don't need to specify the type beforehand (i.e. you would have used just owner, rather than Window owner). And remember you must declare your variables before you use them.

Thirdly, you need to set the size of a window before you will be able to see it.

Fourthly, you don't really want to be using AWT, you should use Swing, and you really don't want to be using a window, a Frame would provide window decorations like scrollbars, a titlebar and a close button at the top.

lemon09 · 10-01-2009, 05:04 AM

@gzunk

but what was wrong if i had made another class.

gzunk · 10-01-2009, 05:26 AM

Nothing inherently wrong, but there can only be one public class per file, and it must have the same name as the file. Your code had two public classes.

Here's another example of how to create a window:

Code:

import javax.swing.*;

public class BetterWindow {

	public static void main(String args[]) {
		
		JFrame jf = new JFrame();
		jf.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
		jf.setSize(300,200);
		jf.setVisible(true);
		
	}	
}

Or this, which does the same thing:

Code:

import javax.swing.*;

public class BetterWindow extends JFrame {

	public BetterWindow() {
		setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
		setSize(300,200);
		setVisible(true);
	}
	
	public static void main(String args[]) {
		BetterWindow bw = new BetterWindow();
	}
	
}

In this second example, I create a class called BetterWindow, which has a constructor that sets the default close operation (what happens when you click on the X button) sets the size of the window and sets the window to be visible.

Then during the main method, this constructor is invoked. In the first example, everything is done in the main method.