CS 1410-20 Lab 10

In this lab, we will explore using the Java Swing GUI toolkit, which offers a highly stateful set of classes and methods.

A Frame

Create a new project and a new class called PhoneBook. Use the following code, and run it:

  import javax.swing.*;
  
  public class PhoneBook {
      public static void main(String[] args) {
          JFrame frame = new JFrame("White Pages");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  
          JLabel label = new JLabel("Phone number...");
          frame.getContentPane().add(label);
  
          frame.pack();
          frame.setVisible(true);
      }
  }

This program does not use the tester library. Instead, it defines a starting point in the normal Java way: by defining a static method (i.e., a function) called main.

How Many Frames?

What happens if you add

  JFrame frame2 = frame;

after the declaration of frame and change frame.getContentPane().add(label) to frame2.getContentPane().add(label)?

What happens if, instead of JFrame frame2 = frame;, you add the declaration

  JFrame frame2 = new JFrame("Other White Pages");

?

After you experiment, get rid of frame.

Multiple Labels

To add multiple labels to a frame, you need to create a Panel and add that to the frame instead. Then, you can add multiple labels to the Panel.

Try this program:

  import javax.swing.*;
  
  public class PhoneBook {
      public static void main(String[] args) {
          JFrame frame = new JFrame("White Pages");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  
          JPanel panel = new JPanel();
          frame.getContentPane().add(panel);
  
          JLabel nameLabel = new JLabel("Name...");
          panel.add(nameLabel);
  
          JLabel numberLabel = new JLabel("Phone number...");
          panel.add(numberLabel);
  
          frame.pack();
          frame.setVisible(true);
      }
  }

Multiple Lines

By default, Panel arranges the things that you add to it left-to-right (until it runs out of space). To have a panel arrange items in a different way, you have to set its layout.

Add

  import java.awt.*;

to the beginning of your program, and then set the panel’s layout before packing the frame:

  panel.setLayout(new GridLayout(2, 1, 0, 0));

The 2 means two lines, and 1 means one column per line. The 0s indicate extra space to put between the rows and columns.

Buttons

Create a button by allocating an instance of the JButton class:

  JButton button = new JButton("Lookup");

Add it to your panel on its own line, below the two labels.

Button Clicks

To handle a button click, you add a listener to the button. A listener is an instance of a class that implements the ActionListener interface as exported by java.awt.event.*.

Here’s a listener class that sets a label string in response to a button click:

  class Lookup implements ActionListener {
      JLabel numberLabel;
      Lookup(JLabel numberLabel) {
        this.numberLabel = numberLabel;
      }
      public void actionPerformed(ActionEvent e) {
          numberLabel.setText("555-1212");
      }
  }

Connect Lookup to button like this:

  button.addActionListener(new Lookup(numberLabel));

Text Fields

Use new JTextField() to create a text field, and substitute it in place of nameLabel.

Change Lookup so that it uses the name in the name field to set numberLabel to “no number for <name>.”