Java 中的快捷键（助记符）

Question

I need help with my homework. I can't seem to make this program work. I just need to put shortcut keys for the compute, reset, and exit buttons.

Compute - Ctrl C Reset - Ctrl R Exit - Ctrl E

If you guys need my professor's instructions, I can provide that as well. here

Here's my code:

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

public class Calculator extends JFrame implements ActionListener{
    JLabel fval,sval;
    JTextField tf1,tf2;
    JButton add,subtract,multiply,divide,compute,reset; 
    String s="";
    JPanel jp = new JPanel();
    Calculator(){
        jp.setLayout(new GridLayout(5,2));
        fval=new JLabel("First Value: ");
        sval=new JLabel("Second Value: ");
        tf1=new JTextField();
        tf2=new JTextField();
        add=new JButton("ADD");
        subtract=new JButton("SUBTRACT");
        multiply=new JButton("MULTIPLY");
        divide=new JButton("DIVIDE");
        compute=new JButton("COMPUTE");
        reset=new JButton("RESET");
        jp.add(fval);
        jp.add(tf1);
        jp.add(sval);
        jp.add(tf2);
        jp.add(add);
        jp.add(subtract);
        jp.add(multiply);
        jp.add(divide);
        jp.add(compute);
        jp.add(reset);
        add.addActionListener(this);
        subtract.addActionListener(this);
        multiply.addActionListener(this);
        divide.addActionListener(this);
        compute.addActionListener(this);
        reset.addActionListener(this);
        this.setTitle("Calculator");
        this.setBounds(10,10,300,300);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setResizable(false);
        add(jp);
        
        //ADD
       Action addAction = new AbstractAction("ADD") {
 
            @Override
            public void actionPerformed(ActionEvent evt) {
                s="ADD";
            }
        };

        String key1 = "ADD";
        add.setAction(addAction);
        addAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_A);
        add.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(
                KeyStroke.getKeyStroke(KeyEvent.VK_A, KeyEvent.CTRL_DOWN_MASK), key1);
        add.getActionMap().put(key1, addAction);
        
        //SUBTRACT
        Action subAction = new AbstractAction("SUBTRACT") {
            @Override
            public void actionPerformed(ActionEvent evt) {
                s="SUBTRACT";
            }
        };
        
        String key2 = "SUBTRACT";
        subtract.setAction(subAction);
        subAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_S);
        subtract.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(
                KeyStroke.getKeyStroke(KeyEvent.VK_S, KeyEvent.CTRL_DOWN_MASK), key2);     
        subtract.getActionMap().put(key2, subAction);
        
        //MULTIPLY
         Action mulAction = new AbstractAction("MULTIPLY") {
            @Override
            public void actionPerformed(ActionEvent evt) {
                s="MULTIPLY";
            }
        };
        
        String key3 = "MULTIPLY";
        multiply.setAction(mulAction);
        mulAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_M);
        multiply.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(
                KeyStroke.getKeyStroke(KeyEvent.VK_M, KeyEvent.CTRL_DOWN_MASK), key3);     
        multiply.getActionMap().put(key3, mulAction);
        
        //DIVIDE
        Action divAction = new AbstractAction("DIVIDE") {
            @Override
            public void actionPerformed(ActionEvent evt) {
                s="DIVIDE";
            }
        };
        
        String key4 = "DIVIDE";
        divide.setAction(divAction);
        divAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_D);
        divide.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(
                KeyStroke.getKeyStroke(KeyEvent.VK_D, KeyEvent.CTRL_DOWN_MASK), key4);     
        divide.getActionMap().put(key4, divAction);
        
    }
    
    public void Add(double n1,double n2){
        JOptionPane.showMessageDialog(this, +(n1+n2), "Answer", JOptionPane.INFORMATION_MESSAGE);
    }
    public void Subtract(double n1,double n2){
        JOptionPane.showMessageDialog(this, +(n1-n2), "Answer", JOptionPane.INFORMATION_MESSAGE);
    }
    public void Multiply(double n1,double n2){
        JOptionPane.showMessageDialog(this, +(n1*n2), "Answer", JOptionPane.INFORMATION_MESSAGE);
    }
    public void Divide(double n1,double n2){
        JOptionPane.showMessageDialog(this, +(n1/n2), "Answer", JOptionPane.INFORMATION_MESSAGE);
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        String in=e.getActionCommand();
        if(in.equals("COMPUTE")){
        try {
            double n1=Double.parseDouble(tf1.getText());
            double n2=Double.parseDouble(tf2.getText());
        
            if(s.equals("ADD"))
                Add(n1,n2);
            else if(s.equals("SUBTRACT"))
                Subtract(n1,n2);
            else if(s.equals("MULTIPLY"))
                Multiply(n1,n2);
            else if(s.equals("DIVIDE"))
                Divide(n1,n2);
            else if(in.equals("RESET")){
                tf1.setText("");
                tf2.setText("");
                s="";
            }else
            {
                s=in;
         }
        }
        catch (NumberFormatException e1) {
            compute.setSelected(true);
        JOptionPane.showMessageDialog(this, "Math Error.", "Warning", JOptionPane.INFORMATION_MESSAGE);
    }
    }       
};
    
    public static void main(String[] args) {
        new Calculator();
    }  
}

Thank you in advance!

Answer 1

I just need to put shortcut keys for the compute, reset, and exit buttons.

I think you are confusing a "mnemonic" with an "accelerator".

The "mnemonic" is invoked when the component is focused. You invoke the Action by using the "Alt" key plus the underlined character of the text on the button.

The "accelerator" can be invoked even when the component doesn't have focus by using the specified KeyStroke.

So instead of attempting use Key Bindings directly, you can set the "accelerator" of the Action . When you add the Action to the button the key bindings will be set automatically for you.

Read the section from the Swing tutorial on How to Use Actions for more information