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Summary - Basic GUI Elements
Posted on: July 27, 2006 at 12:00 AM
Basic GUI Elements

Java: Summary - Basic GUI Elements

In this tutorial we will learn about Basic GUI elements in Java program.

Following table summarizes the variable declarations.

String s; // Any string.
String t; // A string.
//Interpreted as HTML if starts with "<html>" and ends with "</html>".
Font f; // A Font object.
Icon img; // An image.
Container cont; // Container is the superclass of JPanel.

Now let's see the Top-level Container in Swing. JFrame is top level container in Swing.

Following table summarizes the useful methods of JFrame.

Top-level Containers (JFrame)

JFrame - window, typically subclassed
w = new JFrame(); Constructor
w.setTitle(t); Sets titlebar text to t
w.setDefaultCloseOperation(opt); Use opt JFrame.EXIT_ON_CLOSE to terminate program when close box clicked.
w.setResizable(false); Prevent user from resizing window.
w.show(); Use w.setVisible(true) instead.
w.hide(); Use w.setVisible(false) instead.
w.setVisible(true/false); Same as w.show() or w.hide()
w.setContentPane(cont); Sets the content pane - common to pass a JPanel here.
cont = w.getContentPane(); Returns the window's content pane.
w.setJMenuBar(mb); Adds JMenuBar (contains Jmenus, which contain JMenuItems) to window.

Low-level Containers (JPanel)

JPanel - Set layout and add components to JPanel.
p = new JPanel(); Creates new JPanel
p.setLayout(layout); Sets the panel's layout.
p.add(widget); Adds the widget to next position in Layout (eg, Flow, Grid, or Box layouts).
p.add(widget, constraint); Adds the widget to position defined by constraint (eg, Border or Gridbag layouts).

Components (JLabel, JTextField, JButton) and their common methods

cmp.requestFocus(); Puts focus (eg, blinking cursor) in the field, selection of a button, etc.
tf.setFont(f); Sets font.
JLabel - For fixed text.
lbl = new JLabel(t); Creates JLabel with text (can be HTML). Typically created in add() call.
JTextField - Box containing one line of text.
tf = new JTextField(n); Creates textfield about n columns wide.
s = tf.getText(); Returns string in textfield.
tf.setText(s); Sets text to s.
tf.addActionListener(lst); Action listener lst will be called if enter typed.
tf.setEditable(true/false); Don't allow user to edit text field used for output.
tf.setHorizontalAlignment(align); JTextField.LEFT (default), JTextField.CENTER, or JTextField.RIGHT
JButton - Standard clickable button.
btn = new JButton(t); Creates button with text t.
btn = new JButton(act); Creates button from Action act for text, icon, listener, etc.
btn = new JButton(img); Creates button with icon img.
btn = new JButton(t, img); Creates button with both text and icon.
btn.addActionListener(lst); Action listener lst called when button clicked.
btn.setEnabled(true/false); Used to enable/disable button.

Layouts (FlowLayout, BorderLayout, GridLayout, BoxLayout)

FlowLayout - Arranges widgets left-to-right, top-to-bottom.
p.setLayout(new FlowLayout()); Sets layout of the panel to FlowLayout.
BorderLayout - Lays out components in BorderLayout.NORTH, EAST, SOUTH, WEST, and CENTER sections.
p.setLayout(new BorderLayout()); Sets layout of the panel to BorderLayout. Widgets added with constraint.
GridLayout - Lays out components in equal sized rectangular grid, added r-t-l, top-to-bottom.
p.setLayout(new GridLayout(r, c)); Sets layout to GridLayout with specified rows and columns.
p.setLayout(new GridLayout(r, c, h, v)); As above but also specifies horizontal and vertical space between cells.
BoxLayout - Lays out components in a single row or column. Can add "glue" and rigid areas to control spacing.
p.setLayout(new BoxLayout(p, dir)); Layout is horizontal (dir is BoxLayout.X_AXIS) or vertical (BoxLayout.X_AXIS).

Copyleft 2004 Fred Swartz
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