200行Java代码编写一个计算器程序

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.TextField;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.Stack;
import javax.swing.JFrame;
/** * 图形界面的计算器程序，只能计算加减乘除， * 算式中可以有小括号。数字可以是小数 */
public class CalcGUI extends JFrame{
  private static final long serialVersionUID = 1L;
  private TreeNode resultTree;
  private String textFieldString;
  private boolean calcSuccess = true;
  private char ops[][] = {
      {'>','>','<','>'},{'>',{'<','=','E'},{'E','E','='},};
  Stack<TreeNode> nodesStack = new Stack<TreeNode>();
  Stack<Character> opsStack = new Stack<Character>();
  publicstaticvoidmain(String[] args) {
    CalcGUI gui = new CalcGUI();
    gui.userGUI();
  }
  publicvoiduserGUI(){
    this.setLayout(new BorderLayout());
    TextField tf = new TextField("请输入表达式，按Enter开始计算~",40);
    tf.selectAll();
    tf.getText();
    tf.addKeyListener(new KeyAdapter(){
      publicvoidkeyPressed(KeyEvent e){
        if(e.getKeyCode() == KeyEvent.VK_ENTER){
          textFieldString = ((TextField)e.getComponent()).getText();
          calcSuccess = true;
          resultTree = null;
          try{
            resultTree = calc(textFieldString + "#");
          }catch(Exception e1){
            calcSuccess = false;
          }
          CalcGUI.this.repaint();
        }
      }
    });
    this.add(tf,BorderLayout.NORTH);
    this.setSize(500,500);
    this.setTitle("calc GUI");
    this.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
    this.setResizable(true);
    this.setVisible(true);
  }
  private int levelHeight = 60;
  private int diameter = 25;
  publicvoidpaint(Graphics g){
    super.paint(g);
    if(calcSuccess){
      if(resultTree != null){
        g.drawString("计算结果为：" + resultTree.value,10,80);
        int rootBeginX = this.getWidth() / 2;
        int rootBeginY = 100;
        Point p = new Point(rootBeginX,rootBeginY);
        drawTree(g,resultTree,p,this.getWidth() / 2 - 20,p);
      }
    }else{
      g.setColor(Color.RED);
      g.drawString("表达式语法有误！",80);
    }
  }
  privatevoiddrawCircle(Graphics g,Point p,int r){
    g.drawOval(p.x - r,p.y - r,r * 2,r * 2);
  }
  privatevoiddrawTree(Graphics g,TreeNode node,Point pme,int width,Point pfather){
    if(node == null) return;
//   System.out.println("in drawTree,node.value=" + node.value + ",node.op=" + node.op);
    g.setColor(Color.GREEN);
    this.drawCircle(g,pme,diameter / 2);
    g.drawLine(pme.x,pme.y,pfather.x,pfather.y);
    if(node.op != 'E'){
      g.setColor(Color.BLACK);
      g.drawString(String.valueOf(node.op),pme.x,pme.y);
    }else{
      g.setColor(Color.BLACK);
      g.drawString(String.valueOf(node.value),pme.x - diameter / 2,pme.y);
    }
    drawTree(g,node.lft,new Point(pme.x - width / 2,pme.y + levelHeight),width / 2,pme);
    drawTree(g,node.rt,new Point(pme.x + width / 2,pme);
  }
  public TreeNode calc(String inStr) throws Exception{
    opsStack.push('#');
    StringBuilder buf = new StringBuilder();
    int i = 0;
    while(i < inStr.length()){
      if(Character.isDigit(inStr.charAt(i)) || inStr.charAt(i) == '.'){// number
        buf.delete(0,buf.length());
        while(i < inStr.length() && 
            (Character.isDigit(inStr.charAt(i)) || inStr.charAt(i) == '.'))
          buf.append(inStr.charAt(i++));
        Double number = Double.parseDouble(buf.toString());
        nodesStack.push(new TreeNode(number));
      }else if(inStr.charAt(i) == ' '){
        i++;
        continue;
      }else{// operation
        char op = inStr.charAt(i);
        int subNew = getSub(op);
        boolean goOn = true;
        while(goOn){
          if(opsStack.isEmpty())
            throw new Exception("运算符太少！");
          char opFormer = opsStack.peek();
          int subFormer = getSub(opFormer);
          switch(ops[subFormer][subNew]){
          case '=':
            goOn = false;
            opsStack.pop();
            break;
          case '<':
            goOn = false;
            opsStack.push(op);
            break;
          case '>':
            goOn = true;
            TreeNode n1 = nodesStack.pop();
            TreeNode n0 = nodesStack.pop();
            double rs = doOperate(n0.value,n1.value,opFormer);
            nodesStack.push(new TreeNode(rs,opFormer,n0,n1));
            opsStack.pop();
            break;
          default:
            throw new Exception("没有匹配的操作符：" + op);
          }
        }
        i++;
      }
    }
    return nodesStack.pop();
  }
  privatedoubledoOperate(double n0,double n1,char op) throws Exception{
    switch(op){
    case '+': return n0 + n1;
    case '-': return n0 - n1;
    case '*': return n0 * n1;
    case '/': return n0 / n1;
    default: throw new Exception("非法操作符：" + op);
    }
  }
  privateintgetSub(char c){
    switch(c){
      case '+': return 0;
      case '-': return 1;
      case '*': return 2;
      case '/': return 3;
      case '(': return 4;
      case ')': return 5;
      case '#': return 6;
      default : return -1;
    }
  }
}
class TreeNode{
  public double value;
  public char op = 'E';
  public TreeNode lft;
  public TreeNode rt;
  public TreeNode(double value){
    this.value = value;
  }
  public TreeNode(double value,char op,TreeNode lft,TreeNode rt){
    this.value = value;
    this.op = op;
    this.lft = lft;
    this.rt = rt;
  }
  StringBuilder buf = new StringBuilder();
  public String toString(){
    out(this);
    return buf.toString();
  }
  privatevoidout(TreeNode node){
    if(node == null) return;
    out(node.lft);
    if(node.op != 'E')
      buf.append(node.op);
    else
      buf.append(node.value);
    out(node.rt);
  }
}