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Some Examples of Java Graphical User Interface (GUI) Programming

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• Example 2: Scrollable Text Input & Output Areas
  • What are we making:

    • Enter some text in the top window
    • Press the Copy button to find the words in the bottom window

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  • Step 1: make the GUI

    public class CopyText2 { // Components shared by main() and call back methods // must be defined OUTSIDE static JTextArea inputArea; // Text area for input static JTextArea outputArea; // Text area for output static JButton actionButton; // Button to trigger copy action public static void main(String[] args) { JFrame f = new JFrame("TextTest 2"); // +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ // 1. Construct components in the GUI // +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ // ===================================================== // 1. a text area for input // The text area will hold 6 lines or 42 characters // ===================================================== inputArea = new JTextArea(6, 42); // Default is editable... // **************************************************************** // Picks a font for the inputArea // **************************************************************** inputArea.setFont( new Font("SansSerif", Font.BOLD, 17) ); // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv // Add scroll bars to JTextArea // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ JScrollPane inputScrollArea = new JScrollPane(inputArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS); // =========================== // 2. a text area for output // =========================== outputArea = new JTextArea(12, 42); outputArea.setEditable(false); // No editing in output area.... outputArea.setFont( new Font("Monospaced", Font.BOLD, 17) ); // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv // Add scroll bars to JTextArea // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ JScrollPane outputScrollArea = new JScrollPane(outputArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS); // ================================ // 3. a button to start the show // ================================ actionButton = new JButton("Copy !"); // +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ // 2. Place the components in JFrame // +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ // ====================================================== // Pick Layout manager first !!! // ====================================================== f.getContentPane().setLayout(new BorderLayout() ); // ====================================================== // Place the input/output text areas in CENTER // ====================================================== JPanel x = new JPanel(); x.setLayout( new GridLayout(2,1) ); x.add(inputScrollArea); x.add(outputScrollArea); f.getContentPane().add(x, "Center"); // ====================================================== // Place the button in SOUTH // ====================================================== JPanel buttonPanel = new JPanel(); buttonPanel.add(actionButton); f.getContentPane().add(buttonPanel, "South"); f.setSize(500, 500); f.setVisible(true); } }

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  • Step 2: implement the call back functions

    class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent event) { String input; StringTokenizer t; // get user input from text area input = inputArea.getText(); // <------ Get text in JTextArea object // Tokenize the string t = new StringTokenizer(input); // display in result field outputArea.setText(""); // Blank output area while (t.hasMoreTokens()) { outputArea.append(t.nextToken() + "\n"); } } }

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  • Step 3: register the call back function

    public class CopyText2 { // Components shared by main() and call back methods // must be defined OUTSIDE static JTextArea inputArea; // Text area for input static JTextArea outputArea; // Text area for output static JButton actionButton; // Button to trigger copy action public static void main(String[] args) { JFrame f = new JFrame("TextTest 2"); /* ++++++++++++++++++++++++++++++++++++++++++ 1. Construct the components ++++++++++++++++++++++++++++++++++++++++++ */ .... /* ++++++++++++++++++++++++++++++++++++++++++ 3. Register Listener for (some) components ++++++++++++++++++++++++++++++++++++++++++ */ calcButton.addActionListener(new ButtonListener()); // Press to copy ! f.setSize(500, 500); f.setVisible(true); } }

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  • Example Program: (Demo above code)                        
    • Prog file: click here