如何让我的计算器执行计算

Question

我是编程新手，有人可以帮助使这个计算器工作吗？如果单击按钮，此代码会在屏幕上输入内容，但我的挑战是添加，减去，除法和乘法按钮执行其功能。我还是编程新手，请帮忙。

        /*
         * Simple Calculator Program
         * Author : RM
         * Date : 10/7/2016
         * Version : 1.0 
         */
        import java.awt.*;
        import java.awt.event.*;

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

        public class SimpleCalculator2 extends JFrame implements ActionListener{

            private JPanel contentPanel;
            private JPanel buttonPanel;
            private JTextField display;
            private JButton button;
            private String buttonOrder;
            private ActionListener buttonEvent;
            private Font font = new Font ("Ariel", Font.BOLD,52);
        public SimpleCalculator2 (){
                buttonEvent =new EventHandler();
                buttonPanel = new JPanel();
            String buttonOrder ="789+456-123*C0=/";

                    display = new  JTextField();
                    display.setFont(font);
                buttonPanel.setLayout(new GridLayout(4,4));
                for(int i=0; i< buttonOrder.length(); i++)

                {
                    String caption =  buttonOrder.substring (i,i+1);
                            button= new JButton(caption);
                            buttonPanel.add(button);
                            button.setFont(font);
                    button.addActionListener(buttonEvent);
                }

                contentPanel = new JPanel();
                contentPanel.setLayout(new BorderLayout());
                contentPanel.add(display, BorderLayout.NORTH);
                contentPanel.add(buttonPanel, BorderLayout.SOUTH);
                this.setContentPane(contentPanel);
                this.pack();
                this.setTitle("Simple Calculator2");
                 this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                this.setVisible(true);

        }



        public static void main (String args[]){
                new SimpleCalculator2();
            }

            @Override
            public void actionPerformed(ActionEvent e) {
                throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
            }
            public class EventHandler implements ActionListener{
        public void actionPerformed(ActionEvent e){
            display.setText(display.getText() +e.getActionCommand());


        }
            }
            }