java - 如何在Java中获取键盘输入并将其显示在jpanel上

Question

我想知道这是否可行。我正在使用 Java 中的 swing 创建一个基本计算器，到目前为止一切都成功了。我无法完成的是从键盘获取用户输入并将其显示在 jpanel 上。我不知道这是否可能，如果可以，请链接我到任何文章或只是帮助我解决我需要做的事情。谢谢。

Answer 1

以 How to Write a Key Listener 开头和 Code Sample – KeyEventDemo.java .

package events;

/*
* KeyEventDemo
*/

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;

public class KeyEventDemo extends JFrame
        implements KeyListener,
        ActionListener
{
    JTextArea displayArea;
    JTextField typingArea;
    static final String newline = System.getProperty("line.separator");

    public static void main(String[] args) {
        /* Use an appropriate Look and Feel */
        try {
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
            UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        } catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        } catch (IllegalAccessException ex) {
            ex.printStackTrace();
        } catch (InstantiationException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        /* Turn off metal's use of bold fonts */
        UIManager.put("swing.boldMetal", Boolean.FALSE);

        //Schedule a job for event dispatch thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        KeyEventDemo frame = new KeyEventDemo("KeyEventDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Set up the content pane.
        frame.addComponentsToPane();


        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    private void addComponentsToPane() {

        JButton button = new JButton("Clear");
        button.addActionListener(this);

        typingArea = new JTextField(20);
        typingArea.addKeyListener(this);

        //Uncomment this if you wish to turn off focus
        //traversal.  The focus subsystem consumes
        //focus traversal keys, such as Tab and Shift Tab.
        //If you uncomment the following line of code, this
        //disables focus traversal and the Tab events will
        //become available to the key event listener.
        //typingArea.setFocusTraversalKeysEnabled(false);

        displayArea = new JTextArea();
        displayArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(displayArea);
        scrollPane.setPreferredSize(new Dimension(375, 125));

        getContentPane().add(typingArea, BorderLayout.PAGE_START);
        getContentPane().add(scrollPane, BorderLayout.CENTER);
        getContentPane().add(button, BorderLayout.PAGE_END);
    }

    public KeyEventDemo(String name) {
        super(name);
    }


    /** Handle the key typed event from the text field. */
    public void keyTyped(KeyEvent e) {
        displayInfo(e, "KEY TYPED: ");
    }

    /** Handle the key pressed event from the text field. */
    public void keyPressed(KeyEvent e) {
        displayInfo(e, "KEY PRESSED: ");
    }

    /** Handle the key released event from the text field. */
    public void keyReleased(KeyEvent e) {
        displayInfo(e, "KEY RELEASED: ");
    }

    /** Handle the button click. */
    public void actionPerformed(ActionEvent e) {
        //Clear the text components.
        displayArea.setText("");
        typingArea.setText("");

        //Return the focus to the typing area.
        typingArea.requestFocusInWindow();
    }

    /*
     * We have to jump through some hoops to avoid
     * trying to print non-printing characters
     * such as Shift.  (Not only do they not print,
     * but if you put them in a String, the characters
     * afterward won't show up in the text area.)
     */
    private void displayInfo(KeyEvent e, String keyStatus){

        //You should only rely on the key char if the event
        //is a key typed event.
        int id = e.getID();
        String keyString;
        if (id == KeyEvent.KEY_TYPED) {
            char c = e.getKeyChar();
            keyString = "key character = '" + c + "'";
        } else {
            int keyCode = e.getKeyCode();
            keyString = "key code = " + keyCode
                    + " ("
                    + KeyEvent.getKeyText(keyCode)
                    + ")";
        }

        int modifiersEx = e.getModifiersEx();
        String modString = "extended modifiers = " + modifiersEx;
        String tmpString = KeyEvent.getModifiersExText(modifiersEx);
        if (tmpString.length() > 0) {
            modString += " (" + tmpString + ")";
        } else {
            modString += " (no extended modifiers)";
        }

        String actionString = "action key? ";
        if (e.isActionKey()) {
            actionString += "YES";
        } else {
            actionString += "NO";
        }

        String locationString = "key location: ";
        int location = e.getKeyLocation();
        if (location == KeyEvent.KEY_LOCATION_STANDARD) {
            locationString += "standard";
        } else if (location == KeyEvent.KEY_LOCATION_LEFT) {
            locationString += "left";
        } else if (location == KeyEvent.KEY_LOCATION_RIGHT) {
            locationString += "right";
        } else if (location == KeyEvent.KEY_LOCATION_NUMPAD) {
            locationString += "numpad";
        } else { // (location == KeyEvent.KEY_LOCATION_UNKNOWN)
            locationString += "unknown";
        }

        displayArea.append(keyStatus + newline
                + "    " + keyString + newline
                + "    " + modString + newline
                + "    " + actionString + newline
                + "    " + locationString + newline);
        displayArea.setCaretPosition(displayArea.getDocument().getLength());
    }
}