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', 'E', 'E', 'E', '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！", 10, 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.y + levelHeight), 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);  }}