简单的计算器

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

public class jisuanqi extends JFrame {

	JTextField tf = new JTextField();
	JPanel p = new JPanel();
	double a = 0;
	String s, str;

	JButton b0 = new JButton("0");
	JButton b1 = new JButton("1");
	JButton b2 = new JButton("2");
	JButton b3 = new JButton("3");
	JButton b4 = new JButton("4");
	JButton b5 = new JButton("5");
	JButton b6 = new JButton("6");
	JButton b7 = new JButton("7");
	JButton b8 = new JButton("8");
	JButton b9 = new JButton("9");
	JButton b10 = new JButton("+");
	JButton b11 = new JButton("-");
	JButton b12 = new JButton("*");
	JButton b13 = new JButton("/");
	JButton b14 = new JButton(".");
	JButton b15 = new JButton("=");
	JButton b16 = new JButton("Clear");

	public static void main(String[] args) {
		new jisuanqi().launchFrane();

	}

	public void launchFrane() {
		this.setLocation(300, 300);
		this.setSize(300, 400);
		add(tf, BorderLayout.NORTH);
		add(p, BorderLayout.SOUTH);
		p.setLayout(new GridLayout(5, 4));
		p.add(b0);
		p.add(b1);
		p.add(b2);
		p.add(b3);
		p.add(b4);
		p.add(b5);
		p.add(b6);
		p.add(b7);
		p.add(b8);
		p.add(b9);
		p.add(b10);
		p.add(b11);
		p.add(b12);
		p.add(b13);
		p.add(b14);
		p.add(b15);
		p.add(b16);
		pack();
		setVisible(true);
		b0.addActionListener(new BListener());
		b1.addActionListener(new BListener());
		b2.addActionListener(new BListener());
		b3.addActionListener(new BListener());
		b4.addActionListener(new BListener());
		b5.addActionListener(new BListener());
		b6.addActionListener(new BListener());
		b7.addActionListener(new BListener());
		b8.addActionListener(new BListener());
		b9.addActionListener(new BListener());
		b10.addActionListener(new BListener());
		b11.addActionListener(new BListener());
		b12.addActionListener(new BListener());
		b13.addActionListener(new BListener());
		b14.addActionListener(new BListener());
		b15.addActionListener(new BListener());
		b16.addActionListener(new BListener());
		this.addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
		});
	}

	class BListener implements ActionListener {
		public void actionPerformed(ActionEvent e) {
			JButton b = (JButton) e.getSource();
			String s = b.getLabel();
			if (s=="=")
		     {
		      jisuan();
		      s=String.valueOf(a);
		      tf.setText(s);
		      str="";
		     }
		     else if(s=="+")
		     {
		      jisuan();
		      tf.setText("");
		      str="+";
		     }
		     else if(s=="-")
		     {
		      jisuan();
		      tf.setText("");
		      str="-";
		     }
		     else if(s=="*")
		     {
		      jisuan();
		      tf.setText("");
		      str="*";
		     }
		     else if(s=="/")
		     {
		      jisuan();
		      tf.setText("");
		      str="/";
		     }
		     else
		     tf.setText(tf.getText()+s);
		     if(s=="Clear")
		     tf.setText("");
		    }
		    public void jisuan()
		    {
		     if(str=="+")
		     {
		      a+=Double.valueOf(tf.getText());
		     }
		     else if(str=="-")
		     {
		      a-=Double.valueOf(tf.getText());
		     }
		     else if(str=="*")
		     {
		      a*=Double.valueOf(tf.getText());
		     }
		     else if(str=="/")
		     {
		      a/=Double.valueOf(tf.getText());
		     }
		     else
		     {
		      a=Double.valueOf(tf.getText());
		     }
		    }
		   }
}