calculatorpanel.java

设计思路 首先该程序主要知识点就是图形用户界面,对程序界面的基本结构设计如下 建立框架作为可视化程序界面的基本界面,考虑到要在程序中添加各种组件,所以采用面板比较合理,故将类将要继承JPanel类

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

public class CalculatorPanel extends JPanel
	implements ActionListener{
	
	private JTextField display;
	private double arg = 0;
	private String operator = "=";
	private boolean start = true;
	
	public CalculatorPanel(){
		setLayout(new BorderLayout());
		display = new JTextField("0");
		display.setEditable(false);
		add(display,"North");
			
		JPanel p = new JPanel();
		p.setLayout(new GridLayout(4,4));
		String buttons = "789/456*123-0.=+";
		for(int i = 0;i < buttons.length(); i++)
			addButton(p,buttons.substring(i,i + 1));
			
		add(p,"Center");
		}
		
	private void addButton(Container c, String s){
		JButton b = new JButton(s);
		c.add(b);
		b.addActionListener(this);
	}
		
	public void actionPerformed(ActionEvent e){
		String s = e.getActionCommand();
		if ('0' <= s.charAt(0) && s.charAt(0) <= '9' || s.equals(".")){//输出0-9和小数点
			if(start)//输出0-9
				display.setText(s);
			else //输出小数点
				display.setText(display.getText() + s);
			start = false;
		}
		else{//输入加减或负号时的操作
			if(start){
				if(s.equals("-")){//输入负号时的操作
					display.setText(s);
					start = false;
				}
				else operator = s;
			}
			else{//输入加减符号时的操作
				double x = Double.parseDouble(display.getText());
				calculate(x);	
				operator = s;	
				start = true;
			}
		}	
	}
	
	public void calculate(double n){//计算,arg为第一位操作数,n为第二为操作数,开始计算时的第一位操作数arg是0
		if(operator.equals("+")) arg +=n;
		else if (operator.equals("-")) arg -= n;
		else if (operator.equals("*")) arg *= n;
		else if (operator.equals("/")) arg /= n;
		else if (operator.equals("=")) arg = n;
		display.setText("" + arg);
	}
}