SEEM3460 Tutorial

GUI in Java

GUI

Graphical User Interfaces

Some Basic GUI Terms Component (Control in some languages)

the basic GUI unit something visible something that user can make action with

Container component that can hold other components a component hierarchy can be formed

Frame (Form in some languages) window that brings components to the display

Typical Components Button Label TextField (TextBox) Panel List (ListBox) Choice (ComboBox) CheckBox CheckBoxGroup (RadioButton) Menu …

Typical Properties of a GUI unit location size border (color, width, style) background color foreground color text font (name, size, style) components (only for containers) visible: determine whether it is displayed graphic: for custom drawing

Action and Event Different components captures different actions

(e.g. a click, a key press, a mouse move) Actions or program statements raise events Event handler/action listener are classes

which contain methods (actionPerformed(Event) for Java) registered to be invoked when events are raised. This is called event handling

A component can register an action listener to handle all actions it captures

The flow of GUI programs are event-based

Layout: Special from Java

Save programmer’s effort to arrange components by automatically setting the right size and position

Most typical Layout Managers: FlowLayout: Left to right GridLayout: N by M BorderLayout: N, E, S, W, Center

Layout: Examples

import javax.swing.*; import java.awt.*; import java.awt.event.*;

public class Counter extends JFrame {

private int count = 0; private JButton myButton = new JButton("Push Me!"); private JLabel label = new JLabel("Count: " + count);

public Counter () { setLocationRelativeTo(null); // disply to the middle of the screen setDefaultCloseOperation(EXIT_ON_CLOSE); setLayout(new FlowLayout(FlowLayout.LEFT)); //set layout manager add(myButton); //add components add(label);

myButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { count++; label.setText("Count: " + count); } }); pack(); setVisible(true); }

public static void main(String[] args) { new Counter();

} }

Example: Counter.java