calculatorjframe.java

比微软的好些

//【实验6.1】  计算器。

import java.awt.Color;
import java.awt.GridLayout;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

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

public class CalculatorJFrame extends JFrame implements ActionListener
{
    private JTextField text;                               //显示计算结果的文本行

    private char op;                                       //当前运算符
    private float value;                                   //当前计算结果值
    private boolean first;                                 //表示是否为数值的第1个数字
        
    public CalculatorJFrame()
    {
        super("Calculator");
        this.setSize(280,210);
        this.setLocation(300,240);

        this.display();                                    //显示图形用户界面
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setVisible(true);

        op='+';
        value=0.0f;
        first=true;
    }

    private void display()                                 //图形用户界面
    {
        text = new JTextField("0.",30);
        text.setHorizontalAlignment(JTextField.RIGHT);     //设置对齐方式，右对齐
        text.setEditable(false);                           //只能显示，不允许编辑
        this.add(text,"North");

        JPanel panel = new JPanel(new GridLayout(5,4,5,5));
        this.add(panel);
        panel.add(new JButton("sqrt"));
        panel.add(new JButton("+/-"));

        JButton button_backspace = new JButton("Backspace");
        panel.add(button_backspace);
        button_backspace.addActionListener(this);          //为按钮注册单击事件监听器

        JButton button_clear = new JButton("C");
        panel.add(button_clear);
        button_clear.addActionListener(this);
        
        JButton button_seven = new JButton("7");
        panel.add(button_seven);
        button_seven.addActionListener(this);

        JButton button_eight = new JButton("8");
        panel.add(button_eight);
        button_eight.addActionListener(this);

        JButton button_nine = new JButton("9");
        panel.add(button_nine);
        button_nine.addActionListener(this);

        JButton button_division = new JButton("/");
        panel.add(button_division);
        button_division.addActionListener(this);

        JButton button_four = new JButton("4");
        panel.add(button_four);
        button_four.addActionListener(this);

        JButton button_five = new JButton("5");
        panel.add(button_five);
        button_five.addActionListener(this);

        JButton button_six = new JButton("6");
        panel.add(button_six);
        button_six.addActionListener(this);

        JButton button_multiplication = new JButton("*");
        panel.add(button_multiplication);
        button_multiplication.addActionListener(this);

        JButton button_one = new JButton("1");
        panel.add(button_one);
        button_one.addActionListener(this);

        JButton button_two = new JButton("2");
        panel.add(button_two);
        button_two.addActionListener(this);

        JButton button_three = new JButton("3");
        panel.add(button_three);
        button_three.addActionListener(this);

        JButton button_minus = new JButton("-");
        panel.add(button_minus);
        button_minus.addActionListener(this);

        JButton button_zero = new JButton("0");
        panel.add(button_zero);
        button_zero.addActionListener(this);

        JButton button_radixpoint = new JButton(".");
        panel.add(button_radixpoint);
        button_radixpoint.addActionListener(this);

        JButton button_equalto = new JButton("=");
        panel.add(button_equalto);
        button_equalto.addActionListener(this);

        JButton button_plus = new JButton("+");
        panel.add(button_plus);
        button_plus.addActionListener(this);
    }

    public void actionPerformed(ActionEvent e)             //按钮单击的事件处理方法
    {
        String current = e.getActionCommand();             //获取按钮标签
        if (current.equals("C"))                           //清除
        {
            text.setText("0.");                            //重新设置文本内容
            value = 0.0f;
            first = true;
            return;
        }
        
        if (current.equals("Backspace"))                   //退格
        {
            String str=text.getText().substring(0,text.getText().length()-1);
            text.setText(str);
            if (str.equals(""))
            {
                text.setText("0.");
                first = true;
            }
            return;
        }
        
        if (current.compareTo("0")>=0 && current.compareTo("9")<=0   //0~9数字按钮
            || current.equals("."))
        {
            if (first)
            {
                text.setText("");
                first = false;
            }
            text.setText(text.getText()+current);
        }
        else
        {
            System.out.print(""+value+op+text.getText()+"=");
            if (op=='+')
                value += Float.parseFloat(text.getText()); //转换成浮点数后运算 
            if (op=='-')
                value -= Float.parseFloat(text.getText());
            if (op=='*')
                value *= Float.parseFloat(text.getText());
            if (op=='/')
                value /= Float.parseFloat(text.getText());
              
            System.out.println(""+value);
            text.setText(""+value);
            op = current.charAt(0);                        //字符串中取第1个字符
            first = true;
        }
    }

    public static void main(String arg[])
    {
        new CalculatorJFrame();
    }
}

/*
程序设计说明如下。
1、也可以使用双精度浮点数，将字符串转换双精度浮点数的方法如下：
    Double.parseDouble(text.getText())
    
2、switch语句的表达式只能是整数，不能是字符，例如，下列语句的逻辑含义正确，但运算结果不正确。    
                switch (op)
                {
                    case '+': value += Float.parseFloat(text.getText());  //转换成浮点数后运算 
                    case '-': value -= Float.parseFloat(text.getText());
                    case '*': value *= Float.parseFloat(text.getText());
                    case '/': value /= Float.parseFloat(text.getText());
                }

3、错误处理未做
例如，连接单击当数点【.】或【=】按钮等。
*/