（没有括号和优先级，简易计算器）界面：
package javaprogram; import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; class Calculator extends JFrame{ private JLabel showJlabel = new JLabel(); //用来显示数值 //基础组件 private JPanel numJpanel = new JPanel(); //按钮面板 //容器类 private JPanel mainJpanel = new JPanel(); //主面板 private double result; //用来接收计算结果 private String symbol; //用来接收符号 private boolean start; //用来判断是否重新开始 public void init(){//初始化 this.setSize(300,220); //给窗体设置大小 this.setVisible(true); //让窗体可见 this.setLocationRelativeTo(null); //让窗体居中的方法 this.setDefaultCloseOperation(EXIT_ON_CLOSE); //点击退出则程序关闭 this.setTitle("-----中华小妹牌计算器------"); //设置窗体标题 mainJpanel.setLayout(new BorderLayout()); //给主面板设为边框布局 mainJpanel.add(showJlabel,"North"); //让显示框位于主面板北方 mainJpanel.add(numJpanel);//在主面板中添加按钮面板 this.add(mainJpanel); symbol ="=";//默认 showJlabel.setText("0"); //给显示框设置默认值0 showJlabel.setForeground(Color.blue); start=true; //默认开始 numJpanel.setLayout(new GridLayout(5,4));//将界面划分成5行4列 Action1 action1 = new Action1();//添加数字和归零符号等处理 //准备监听对象 Action2 action2 = new Action2();//添加运算符号 this.addButton("C",action1);//归0 this.addButton("/",action2); this.addButton("*",action2); this.addButton("BACK",action1);//清除打错的字符 this.addButton("7",action1); this.addButton("8",action1); this.addButton("9",action1); this.addButton("+",action2); this.addButton("4",action1); this.addButton("5",action1); this.addButton("6",action1); this.addButton("-",action2); this.addButton("1",action1); this.addButton("2",action1); this.addButton("3",action1); this.addButton("%",action2); this.addButton(".",action1); this.addButton("0",action1); this.addButton("=",action2); this.addButton("",action1); } //添加按钮并给按钮设置监听方法 监听按钮 public void addButton(String string,ActionListener a1){ JButton button =new JButton(string);//创建一个有标签文本、无图标的按钮 button.addActionListener(a1); numJpanel.add(button); } //数字和基本操作处理 class Action1 implements ActionListener{ //接收操作事件的监听器接口 public void actionPerformed(ActionEvent e){ //同一个JFrame里可能有多个按钮的事件，为了避免冲突，给每个按钮设置不同的ActionCommand String input = e.getActionCommand();//获取事件的标签内容 if(showJlabel.getText().equals("0")){ start = true; } if(start){ //如果start是true，就表示重新开始输入新的数 showJlabel.setText(""); start = false; } if(!input.equals("BACK")&&!input.equals("C")) { //更新文本内容 showJlabel.setText(showJlabel.getText() + input); } if(input.equals("C")){//归0操作 showJlabel.setText("0"); } if(input.equals("BACK")){ //回退操作 if(showJlabel.getText().length()>1){ showJlabel.setText(showJlabel.getText().substring(0, showJlabel.getText().length()-1)); //substring(0,3)string从0截取截到2 } else{ showJlabel.setText("0"); } } } } //进行运算 class Action2 implements ActionListener{ public void actionPerformed(ActionEvent e){ String input = e.getActionCommand();//获取事件的标签内容 if(start){ symbol = input; //符号 }else{ if(symbol.equals("+")){ result += Double.parseDouble(showJlabel.getText()); //将String类型的数字转换为double型的数字 } else if(symbol.equals("-")){ result -= Double.parseDouble(showJlabel.getText()); } else if(symbol.equals("*")){ result *= Double.parseDouble(showJlabel.getText()); } else if(symbol.equals("/")){ result /= Double.parseDouble(showJlabel.getText()); } else if(symbol.equals("%")){ result %= Double.parseDouble(showJlabel.getText()); } else{//等于 “=” 直接显示输出的值 result = Double.parseDouble(showJlabel.getText()); } showJlabel.setText(result+""); symbol = input; start = true; } } } public static void main(String[] args) { Calculator calculator=new Calculator(); calculator.init(); } }