Java Windows - Graphical User Interface Basics

In this tutorial will will deal with Java graphical interface building only - there will be no mention of jMusic. Remember that working in jMusic IS working in Java, so from time to time this diversion into programming with no musical outcome is necessary. Please bear with us.

One of the nice aspects of using Java is that the Graphical User Interface (GUI) code is cross platform. It will run equally well, without change, on any operating system that runs Java, including Windows, Mac OS, Linux, and Solaris.

These GUI examples use the Advanced Windowing Toolkit (AWT) based on Java version 1.1. So make sure your Java version is at that version number or greater. It is a very good idea to have a good Java book handy for this section which deals with the AWT. The examples in this tutorial are based on John Hubbard's "Programming With java" McGraw-Hill, 1999, which is a concise and affordable introduction to application programming in Java.

TestFrame

The results of this simple class will look like this on a Mac:

The advantage of AWT is that it will change to suit the look and feel of the Operating System.  For example, in Windows, the borders/title bar etc will take on the look and feel of a typical Windows window.

Let's have a closer look.

import java.awt.Frame;
 
public class TestFrame{
         public static void main(String[] args) {
                  Frame f = new Frame("Ex. 9.1");
                  f.setSize(250,100);
                  f.setVisible(true);
         }
}

This class first imports the Frame class from the AWT. Window drawing usually starts with a frame.

The main() method creates an instance of a Frame called 'f' and gives it a title. It next sets the dimensions of the frame (window) and finally make sure we can see it.

MyFrame

The results of this simple class will look like this.

import java.awt.Frame;
import java.awt.Color;
 
public class MyFrame extends Frame{
         public MyFrame(String s) {
                  super(s);
                  setBackground(Color.blue);
                  setSize(250,100);
                  setVisible(true);
         }
}
 
//a second class does not need to redefine 
//the import or public status of the class
class TestMyFrame {
         public static void main(String[] args) {
                  new MyFrame("Ex. 9.2");
         }
}
 

This program creates a frame with a blue background. In the process it treats frames in a more interesting way and uses two classes to do so.

Firstly, the Frame and Color classes are imported.

The MyFrame class is decalared as an extension of Frame. This means that it will inherit the attributes of the Frame class. Most significantly we don't need to create an instance of the Frame class directly, rather, we create an instance of the MyFrame class. Thus there is a MyFrame constaructor method. This takes a String argument which is the window title. The super class (Frame) is called with a title - this decalres the window. next the background, sive, and visibility of the window are set.

The TestMyFrame class is a second class which simply calls the MyFrame class and passes it a title string.

Copy this code into a file called MyFrame.java, compile this code two class files will be created. Run the TestMFrame class.

ColoredFrame

The results of this simple class will look like this.

import java.awt.Frame;
import java.awt.Color;
 
public class ColoredFrame extends Frame{
         public ColoredFrame(String s, Color c, int x, int y) {
                  super(s + c.toString());
                  setBackground(c);
                  setSize(350,100);
                  setLocation(x,y);
                  setVisible(true);
         }
}
 
//a second class does not need to redefine 
//the import or public status of the class
class TestColoredFrame {
         public static void main(String[] args) {
                  new ColoredFrame("Ex. 9.3 Red", Color.red, 0, 0);
                  new ColoredFrame("Ex. 9.3 Green", Color.green, 100, 100);
         }
}

This application is a small extension of the previous one. The constructor of the ColoredFrame class takes four arguments, title, color, width, and height. The leverage of multiple classes can be seen in the simplicity in the TestColoredFrame class of creating two (in theory any number) of instances of the ColoredFrame class.

Multiple Frames and Random Colours

In this variation on the code a for-loop is used to create many windows, and a random function is used to create colours and locations. 

import java.awt.Frame;
import java.awt.Color;
 
public class MyFrame extends Frame{
    
    public static void main(String[] args) {
        for(int i=0; i<20; i++) {
            new MyFrame("Frame " + i);
        }
    }
 
    public MyFrame(String s) {
        super(s);
        setBackground(new Color((float)Math.random(), 
                                (float)Math.random(), 
                                (float)Math.random()));
        setSize(250,100);
        setLocation((int)(Math.random() * 600), (int)(Math.random() * 400));
        setVisible(true);
    }
}
 

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© 2003 Andrew R. Brown