How I do Interpreter Pattern: Calculator javacode

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Java

From java code how i can make it in Interpreter Pattern .......
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package test;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Calculator extends JPanel implements ActionListener {
private JTextField display = new JTextField("0");

private String buttonText = "789/456*123-0.=+";

private double result = 0;

private String operator = "=";

private boolean calculating = true;

public Calculator() {
setLayout(new BorderLayout());

display.setEditable(false);
add(display, "North");

JPanel p = new JPanel();
p.setLayout(new GridLayout(4, 4));

for (int i = 0; i < buttonText.length(); i++) {
JButton b = new JButton(buttonText.substring(i, i + 1));
p.add(b);
b.addActionListener(this);

}
add(p, "Center");
}

public void actionPerformed(ActionEvent evt) {
String cmd = evt.getActionCommand();
if ('0' <= cmd.charAt(0) && cmd.charAt(0) <= '9' || cmd.equals(".")) {
if (calculating)
display.setText(cmd);
else
display.setText(display.getText() + cmd);
calculating = false;
} else {
if (calculating) {
if (cmd.equals("-")) {
display.setText(cmd);
calculating = false;
} else
operator = cmd;
} else {
double x = Double.parseDouble(display.getText());
calculate(x);
operator = cmd;
calculating = true;
}
}
}

private void calculate(double n) {
if (operator.equals("+"))
result += n;
else if (operator.equals("-"))
result -= n;
else if (operator.equals("*"))
result *= n;
else if (operator.equals("/"))
result /= n;
else if (operator.equals("="))
result = n;
display.setText("" + result);
}

public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setTitle("Calculator");
frame.setSize(200, 200);
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});

Container contentPane = frame.getContentPane();
contentPane.add(new Calculator());
frame.show();
}
}