java版的计算器（带GUI）

用java做一个简单的计算器

首先是做界面

先定义一些基本数据类型

	JTextField text = new JTextField();
	JPanel p1,p2;//上下两个面板p1和p2
	JButton b[] = new JButton[16];
	String s;//从文本框读的字符串

添加最上面的文本框：

         p1.setLayout(new BorderLayout());
		 text = new JTextField();
		 //重新定义长度和宽度
		 text.setPreferredSize(new Dimension(30,30));
		 p1.add(text);
	    this.add(p1,BorderLayout.NORTH);

添加下方按钮：

        p2.setLayout(new GridLayout(3,5,3,3));//网格式布局，三行五列
		String str [] = {"0","1","2","3","4","5","6","7",
				"8","9","+","-","*","/",".","="};
		ActionListener command=new command();
			for(int i = 0;i<str.length;i++)
		{
			b[i] = new JButton(str[i]);
			b[i].addActionListener(command);//监听
//			b.setSize(50, 20);
			p2.add(b[i]);
		}
		this.add(p2);

监听事件函数command

class command implements ActionListener{

		@Override
		public void actionPerformed(ActionEvent e) {
			// TODO Auto-generated method stub
			String s = e.getActionCommand();//获取每次输入的内容
			if(s.equals("="))
			{
				s=text.getText();//获取文本框的内容
				//直接使用第三方库import javax.script.*，下面有解释
				ScriptEngine js = new    ScriptEngineManager().getEngineByName("JavaScript");
				try {
                    //System.out.print(js.eval(s));
					//将Int转为string		
                    //text.setText(js.eval(s)+"")，num + ""型转换
                    //int.toString()型转换
					text.setText(js.eval(s).toString());
				} catch (ScriptException e1) {
					e1.printStackTrace();
				}
			}
			
			//如果还没有输入等号，在文本框显示内容即可
		    	else{
			text.setText(text.getText()+s);	
			}
		}

运行结果：

对ScriptEngine还有困惑的话，再演示一下import javax.script.*的使用过程，加深印象：

import javax.script.*;
public class day_2 {
	public static void main(String []args) {
       String s1="24+23";
       String s2="24-2";
       String s3="24*2";
       String s4="24/2";
   ScriptEngine js = new ScriptEngineManager().getEngineByName("JavaScript");
      try {
	      System.out.println(s1+"="+js.eval(s1));
	      System.out.println(s2+"="+js.eval(s2));
	      System.out.println(s3+"="+js.eval(s3));
	      System.out.println(s4+"="+js.eval(s4));
      } catch (ScriptException e) {
	      e.printStackTrace();
            }
      }
}

输出结果：

可运行源代码：

import java.awt.*;
import java.awt.event.*;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.swing.*;
import javax.swing.border.Border;
import org.eclipse.swt.widgets.Layout;
public class day_1 extends JFrame {
	JTextField text = new JTextField();
	JPanel p1,p2;
	JButton b[] = new JButton[16];
	String s;
	day_1(){
		super("check !");
		JPanel p1 = new JPanel();
		JPanel p2 = new JPanel();
		p1.setLayout(new BorderLayout());
		text = new JTextField();//此处定义不用JTextField
		//否则引发空指针异常
       text.setPreferredSize(new Dimension(30,30));
		p2.setLayout(new GridLayout(3,5,3,3));
		String str [] = {"0","1","2","3","4","5","6","7",
				"8","9","+","-","*","/",".","="};
		ActionListener command=new command();
		for(int i = 0;i<str.length;i++)
		{
			b[i] = new JButton(str[i]);
			b[i].addActionListener(command);
//			b.setSize(50, 20);
			p2.add(b[i]);
		}
	    p1.add(text);
	    this.add(p1,BorderLayout.NORTH);
		this.add(p2);
		this.setSize(300,300);
		this.setLocationRelativeTo(null);
		this.setVisible(true);
	}
	class command implements ActionListener{
		@Override
		public void actionPerformed(ActionEvent e) {
			// TODO Auto-generated method stub
			String s = e.getActionCommand();
			if(s.equals("="))
			{
				s=text.getText();
				ScriptEngine js = new ScriptEngineManager().getEngineByName("JavaScript");
				try {
//					System.out.print(js.eval(s));
					
					//将Int转为string		
//					text.setText(js.eval(s)+"");
					
					text.setText(js.eval(s).toString());
				} catch (ScriptException e1) {
					// TODO Auto-generated catch block
					e1.printStackTrace();
				}
			}
			else{
			text.setText(text.getText()+s);	
			}
		}
	}
	public static void main(String []args) {
		new day_1();
	}
}