200行Java代码编写一个计算器程序

发现了大学时候写的计算器小程序，还有个图形界面，能够图形化展示表达式语法树，哈哈;)

只有200行java代码，不但能够计算加减乘除，还能够匹配小括号~

代码点评：

从朴素的界面配色到简单易懂错误提示，无不体现了“用户体验”至上的设计理念；代码异常处理全面合理、滴水不漏，代码缩进优雅大方，变量命名直观易懂；再结合长度适中简单明了的注释，程序整体给人一种清新脱俗之感。背后不难看出作者对学习的热爱以及对设计的苛求，工匠精神可见一斑，真可谓是大学数据结构学以致用的典范！

 

实现代码如下所示：

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);
  }
}

总结

以上所述是小编给大家介绍的200行java代码编写一个计算器程序，希望对大家有所帮助