houzui.java

这是一个简单的计算器

import java.io.*;
import java.util.*;
/**
 * <p>Title: </p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2006</p>
 * <p>Company: </p>
 * @author not attributable
 * @version 1.0
 */

public class houzui {
    Stack store=null;
    
    //构造器
    public houzui() {
        store=new Stack();
    }
    
    /***********************
   算法：
     1 读入运算对象，直接输出
     2 ( 运算符进栈
     3 ) 运算符，栈内的最上一个( 以上的运算符退栈，(也退栈
     4 读入运算符，进入运算栈
       4.1 后进栈的运算符 > 先进栈的运算符，运算符进栈  (优先级比较)
       4.2 后进栈的运算符 <= 先进栈的运算符，将栈内的运算符退栈输出，再进
     5 # 结束符
     ************************/
    
    //接收窗口的输入，并将其转换成后缀表达式
    private String getInput(String qianzhui){
        //将输入的前缀表达式转化成后缀表达式
        store.Push("&");
        String str=qianzhui, f="",h=f;
        
        //括号匹配
        int kl=0,kr=0,kf=0;
       for(int i=0;i<str.length();i++)
       {
            if(str.charAt(i)=='(')
               kl++;
            if(str.charAt(i)==')')
               kr++;
            if(str.charAt(i)=='+'||str.charAt(i)=='-'||
                    str.charAt(i)=='*'||str.charAt(i)=='/')
                kf++;
       }
        if(kl!=kr||kf==0)return "Error";
        
        StringTokenizer m=new StringTokenizer(str);
        
        while(m.hasMoreTokens()){
            f=m.nextToken();
            if(IsAChar(f))
                switch(f.charAt(0)){
                    case '&'://5
                        while(store.Top().charAt(0)!='&')
                            h+=store.Pop()+" ";
                        store.Pop();
                        break;
                    case '('://2
                        store.Push(f);
                        break;// 3 + 4 / ( 25 - ( 6 * 5 ) )  * 8 
                        //-3.4000000000000004
                    case ')'://32 * ( 8 * ( 4 * 2 / 8 - 2 ) + 3 )//-160
                        while(store.Top().charAt(0)!='(')
                            h+=store.Pop()+" ";
                        store.Pop();
                        break;
                    case '*'://4.1
                    case '/':
                        if(store.Top().charAt(0)=='*'||store.Top().charAt(0)=='/')
                            h+=store.Pop()+" ";
                        store.Push(f);
                        break;
                    case '+'://4/2
                    case '-':
                        while(store.Top().charAt(0)!='&'&&store.Top().charAt(0)!='(')
                            h+=store.Pop()+" ";
                        store.Push(f);
                        break;
                } else//1
                    h+=f+" ";
        }
        
        return h+'&';
    }
    
    //input a String
    String inputAString(){
        String aim=" ";
        try{
            BufferedReader in=
                    new BufferedReader(new InputStreamReader(System.in));
            aim=in.readLine();
        }catch(IOException e){e.printStackTrace();}
        return aim+ " &";
    }
    
    boolean IsAChar(String come){
        if(come.length()>1)
            return false;
        if(Character.isDigit(come.charAt(0)))
            return false;
        return true;
    }
    
    /******************************
     *将操作数放入堆栈，
     * 取出两个数，按照紧接他们的操作符进行计算
     ******************************/
    
    //对后缀表达式进行计算，并给出计算结果
    public String outResult(String houzhui){
        String Get=getInput(houzhui),
                c=" ";
        if(Get.equals("Error"))
            return "Error!!! 表达式有误。";

        char done=' ';
        double a=0,b=0;
        double result=0;
        
        StringTokenizer m=new StringTokenizer(Get);
        
        while(m.hasMoreTokens()){
            c=m.nextToken();
            if(IsAChar(c))
                switch(c.charAt(0)){
                    case '&':
                        result=Double.parseDouble(store.Pop());
                        break;
                    case '+':
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        a=Double.parseDouble(store.Pop());
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        b=Double.parseDouble(store.Pop());
                        store.Push(a+b+"");
                        break;
                    case '-':
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        a=Double.parseDouble(store.Pop());
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        b=Double.parseDouble(store.Pop());
                        store.Push(b-a+"");
                        break;
                    case '*':
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        a=Double.parseDouble(store.Pop());
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        b=Double.parseDouble(store.Pop());
                        store.Push(a*b+"");
                        break;
                    case '/':
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        a=Double.parseDouble(store.Pop());
                        if(a==0)
                           return "Error!!! 除数为零。";
                        if(store.Top()==null)return "Error!!!表达式有误。";
                        b=Double.parseDouble(store.Pop());
                        store.Push(b/a+"");
                        break;
                } else
                    store.Push(c+"");
        } 
        
        return ""+result;
    }
    
    
   
            
//  I'll use the Chain structure to make a stack
            class Stack {
//  the node class of the Chain.
        class Node{
            String data="";
            Node link=null;
            
            Node(String newData,Node newLink){
                data=newData;
                link=newLink;
            }
        }
        // the head point
        Node first=null;
        
        //put the data pushed before the first node
        public void Push(String newData){
            first=new Node(newData,first);
        }
        
        //pop the first node, and return that data
        public String Pop(){
            if(first!=null){
                Node m=first;
                first=first.link;
                return m.data;
            }
            return null;
        }
        
        //the top element of stack
        public String Top(){
            if(first!=null)
                return first.data;
            return null;
        }
        
    }
}