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Chapter 4 is all about Java Swing. To make your first GUI (graphical user interface) application you need to import the package javax.swing.JFrame. Here is an example of an empty window:

1public class MyFirstWindow extends JFrame {
2  public static void main(String[] args) {
3    new MyFirstWindow();
4  }
5  public MyFirstWindow() {
6    setSize(300, 300);
7    setTitle("MyFirstWindow");
8    setVisible(true);
9    setDefaultCloseOperation(EXIT_ON_CLOSE);
10    setLocationRelativeTo(null);
11    //this one is not necessary, but places the JFrame in the middle of the screen
12  }

Here, the class MyFirstWindow inherits, thanks to the extends keyword, all of properties and methods of the JFrame. That means an object of a MyFirstWindow is also, in essense, and object of JFrame. But what is JFrame? A JFrame is one of the main JComponents in Java Swing, and you will be using it for all of your GUIs. And, just as a frame of reference, a JComponent is another, more scientific, way of saying every component you will ever use. The difference is in the custom methods of MyFirstWindow such as the constructor, where the title, size, and visibility are set. You may say that setTitle, setSize, and setVisible do not exist, but they are extended JFrame methods. setDefaultCloseOperation(EXIT_ON_CLOSE), meanwhile just ensures that the Java app doesn't lay running hidden in the background.

The code above should output this when run:

An empty window

Colouring these Windows

These windows are not limited to a dull, boring grey, in fact these windows can be set to pretty much any colour under the Sun. To do this you will have to import Color, using the import:

1import java.awt.Color;

To use this import you will have to use the following syntax:

2// this will create a yellow window, however you can replace this with other colours.

As you can see, you can change the colour of your background using the method setBackground(Colour). There are wide range of existing colours like:

Color.PINK, Color.GREEN, Color.BLACK, Color.YELLOW, Color.BLUE, Color.RED, Color.WHITE, Color.CYAN, Color.ORANGE

N.B. American spellings apply here.

This particular piece of code would putput the following:

Coloured window

Ex 1

Copy & run the code. Play around with setSize, setTitle, setVisible and setBackground().

Ex 2

Research the setResizable() method and create another window called MySecondWindow which cannot be resized. HINT: You don't actually need to research it, it either can or cannot be resized (think about how setVisible works).

Well that's nice, but what can you put in these frames? →