calculatorapplet.java

这是一个用JAVA开发有的一个关于计算器的使用

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class CalculatorApplet extends Applet implements ActionListener
{
	// 弹出的窗口
	private Frame calcFrame = new CalculatorFrame();
 public void init()
  {
		// 弹出的按键
		Button calcButton = new Button("Calculator");
		calcButton.addActionListener(this);
		add(calcButton);
  }
 public void actionPerformed(ActionEvent evt)
 {
		// 弹出窗口如果没有被显示，则显示它，否则关闭它
 if (calcFrame.isVisible())
	calcFrame.setVisible(false);
 else
	calcFrame.setVisible(true);
 }
}
class CalculatorFrame extends Frame	implements ActionListener
{
	private TextField display = null;
	private double arg1 = 0;
	private StringBuffer arg2 = new StringBuffer();
	private char op = '=';
  public CalculatorFrame()
  {
		setTitle("Calculator");
		setSize(200, 200);
		setLayout(new BorderLayout());
		// 输出窗口
		display = new TextField("0");
		display.setEditable(false);
		add(display, "North");
		// 数字按键盘
		Panel keypad = new Panel();

		keypad.setLayout(new GridLayout(4, 4));
			// 添加数字和运算符按键
		String keys = "789/456*123-0.=+";
		for (int i = 0; i < keys.length(); i++)
		{
			Button btn = new Button(keys.substring(i, i+1));
			keypad.add(btn);
            // 为按键添加事件监听器
			btn.addActionListener(this);
		}
		            add(keypad, "Center");
   }
 public void actionPerformed(ActionEvent evt)
  {
		// 响应按键，如果是数字则连接到StringBuffer中，
		// 如果是运算符则进行运算。
		String key = evt.getActionCommand();
		char c = key.charAt(0);
		if ((c >= '0'  && c <= '9') || c == '.' ||
			(c == '-' && arg2.length() == 0))
		{
			arg2.append(c);
			display.setText(arg2.toString());
        }
		else
		{
			calculate(Double.parseDouble(arg2.toString()));
			op = c;
			arg2.setLength(0);
			if (c == '=')
				arg2.append(arg1);
		}
	}
 public void calculate(double arg2)
	{
    // 计算
		switch (op)
		{
			case '+': arg1 += arg2;
			          break;
			case '-': arg1 -= arg2;
			          break;
			case '*': arg1 *= arg2;
			          break;
			case '/': arg1 /= arg2;
			          break;
			case '=': arg1 = arg2;
			          break;
			default: break;
         }

		 display.setText(""+arg1);
	  }
 }