Java gui swing计算器操作符

Question

我正试图找出如何在当前代码中实现几个按钮，但经过多次尝试后，我似乎无法找到答案。我需要做以下工作：

所以我的问题是：当我把两个数字加在一起，如果它们不是0（例如x=10和y=10），当我点击加号按钮时，y字段中的内容消失了，我该如何解决这个问题

另外，我的清除按钮不能清除x、y和结果字段中的所有内容，我该如何解决这个问题

如何右对齐x和y字段

package democalc;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EtchedBorder;


class Calculator implements ActionListener {

    private JFrame frame;
    private JTextField xfield, yfield;
    private JLabel rslt;
    private JButton multiButton, clearButton, addButton, subButton, divideButton;
    private JPanel xpanel, buttonPanel;

    public Calculator() {

        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());

        xpanel = new JPanel();
        xpanel.setBorder(new EtchedBorder());
        xpanel.setLayout(new GridLayout(3, 2));

        xpanel.add(new JLabel("x ="));
        xfield = new JTextField("0", 5);
        xpanel.add(xfield);

        xpanel.add(new JLabel("y ="));
        yfield = new JTextField("0", 5);
        xpanel.add(yfield);

        xpanel.add(new JLabel());
        rslt = new JLabel("0");
        rslt.setBackground(Color.green);
        rslt.setBorder(new EtchedBorder());
        rslt.setOpaque(true);
        xpanel.add(rslt);
        frame.add(xpanel, BorderLayout.NORTH);

        buttonPanel = new JPanel();
        frame.add(buttonPanel, BorderLayout.CENTER);

        buttonPanel.add(addButton = new JButton("+"));
        addButton.addActionListener(this);

        buttonPanel.add(subButton = new JButton("-"));
        subButton.addActionListener(this);

        buttonPanel.add(multiButton = new JButton("*"));
        multiButton.addActionListener(this);

        buttonPanel.add(divideButton = new JButton("/"));
        divideButton.addActionListener(this);

        buttonPanel.add(clearButton = new JButton("Clear"));
        clearButton.addActionListener(this);

        frame.pack();
        frame.setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {

        int x = 0, y = 0;

        try {
            String xStr = xfield.getText();
            x = Integer.parseInt(xStr);
        }
        catch (NumberFormatException e) {
                // The string xStr is not a legal number.
            rslt.setText("Illegal data for x.");
            xfield.requestFocusInWindow();
            return;
        }

        /* Get a number from yfield in the same way. */

        try {
            String yStr = yfield.getText();
            y = Integer.parseInt(yStr);
        }
        catch (NumberFormatException e) {
            rslt.setText("Illegal data for y.");
            yfield.requestFocusInWindow();
            return;
        }

        /* Perform the operation based on the action command
             from the button.  Note that division by zero produces
             an error message. */

        String op = event.getActionCommand();
        if (op.equals("+"))
            rslt.setText( "x + y = " + (x+y) );
        else if (op.equals("-"))
            rslt.setText( "x - y = " + (x-y) );
        else if (op.equals("*"))
            rslt.setText( "x * y = " + (x*y) );
        else if (op.equals("/")) {
            if (y == 0)
                rslt.setText("ERROR");
            else
                rslt.setText( "x / y = " + (x/y) );


        }

        if (event.getSource() == clearButton)
            xfield.setText("0");
            yfield.setText("0");


    }
}