Java 7 for Absolute Beginners

CHAPTER 7 ■ WRITING A USER INTERFACE

Swing includes the concept of .a “layout.” A layout. is an object that defines the relationship

between other objects. For example, if you use a BoxLayout object, your components go in a line either

horizontally or vertically. A grid layout, on the other hand, creates a layout that looks like a table (a

number of cells wide by a number of cells high). Java also has a number of other layouts. We use a

number of them in this chapter and later in the book. One handy thing about layouts is that you can use

layouts within layouts. For example, you might use a BoxLayout object set to vertical and then use a

number of other BoxLayouts, each set to horizontal, to add rows of components to your window. You

can achieve a similar effect with a GridLayout object, too, but the BoxLayout with BoxLayout scheme

might work better if you have different numbers of objects to put in each row.

I can go on for a long time (probably for a whole book) about all the options available in Swing, but

I'll mention just one more that may be of interest to you. Swing includes different looks for programs. If

you use the default settings (as I do in this chapter), you get Java's Metal look, which is meant to look the

same on all operating systems. To get the native layout for any given operating system, use the

SystemLookAndFeel object. If you use SystemLookAndFeel, people who use your software on Windows get

a Windows look and feel, whereas users on other operating systems get the look and feel of those

operating systems. The down side is that if Java can't figure out the look and feel of the system, your

program doesn't work. That's why so many Java programs (especially those written for demonstrations

and books) use the default (Metal) look and feel. Still, if you're writing software just for yourself or for a

group of users who use the same operating system, and you can be sure that Java supports that

operating system's look and feel, you can make your programs look just like the other programs that run

on that operating system.

Now, let's do a little more with our program. Let’s start by adding a feature many programs have, a

menu. Listing 7.2 shows how to add .a menu.

Listing 7-2. A Swing program with a menu

package com.apress.java7forabsolutebeginners.examples.swingdemo;

import java.awt.Dimension;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.JFrame;

import javax.swing.JMenu;

import javax.swing.JMenuBar;

import javax.swing.JMenuItem;

public class SwingDemo implements ActionListener {

private JFrame frame = new JFrame("SwingDemo");

private void addMenu(JFrame frame) {

JMenu file = new JMenu("File");

file.setMnemonic('F');

JMenuItem exitItem = new JMenuItem("Exit");

exitItem.setMnemonic('x');

exitItem.addActionListener(this);

file.add(exitItem);

JMenuBar menuBar = new JMenuBar();