表达式计算器java实现

    去年写的一个表达式计算器程序，支持+、-、*、%运算，代码很乱不好理解，不过可以正确运行，贴出来希望可以供大家参考。其中的LinkStack是一个栈，也是自己写的，一块贴出来。

Calculator.java

 

import java.util.*;

public class Calculator{

    public static String transform(String input){

        StringBuffer sb=new StringBuffer();

        LinkStack<Character> stack=new LinkStack<Character>();

        int charcount=input.length();

        char topOperator;

        String date="";

        for(int i=0;i<charcount;i++){

            char test=input.charAt(i);

            if(test>='0'&&test<='9'){

                date=date+test;

                continue;

                }

            else{

                if (date!="") {

                    sb.append(date+",");

                }

                date="";

                if(stack.Empty()){stack.push(test);continue;}

                switch(test){

                    case '+':

                    case '-':

                    case '*':

                    case '/':{

                            while(!stack.Empty()){

                                topOperator=stack.peek();

                                if(precedence(test)<=precedence(topOperator)){

                                    sb.append(stack.pop()+",");

                                } else {

                                    break;

                                }

                            }

                            stack.push(test);

                            break;

                        }

                    case '(':{stack.push(test);break;}

                    case ')':{

                            while((topOperator=stack.pop())!='(')

                                {

                                    sb.append(topOperator+",");

                                }

                                break;

                            }

                    default:break;



                    }

                }

            }

        sb.append(date+",");

        while(!stack.Empty()){

            sb.append(stack.pop()+",");

            }

        return sb.toString();

    }

    public  static int count(String input){

        LinkStack<Integer> stack=new LinkStack<Integer>();

        String[] str=input.split(",");

        int result=0;

        for(int i=0;i<str.length;i++){

            if(!str[i].equals("")){

                if(!str[i].equals("+")&&!str[i].equals("-")&&!str[i].equals("*")&&!str[i].equals("/")){

                    stack.push(Integer.parseInt(str[i]));

                                }

                else{

                    if(!stack.Empty()){

                        int num1=stack.pop();

                        int num2=stack.pop();

                        switch(str[i].charAt(0)){

                            case '+':{result=num2+num1;break;}

                            case '-':{result=num2-num1;break;}

                            case '*':{result=num2*num1;break;}

                            case '/':{result=num2/num1;break;}

                            }

                    stack.push(result);

                    }

                }

            }

        else

            continue;

        }

        return result;

    }

    public  static int precedence(char ch){

        int pre=0;

        switch(ch){

                case '(': return pre=0;

                case '+':

                case '-': return pre=1;

                case '*':

                case '/': return pre=2;

            }

        return pre;

        }

    public static void main(String[] str){

        Scanner input=new Scanner(System.in);

        String st=input.nextLine().toString();

        String[] s=transform(st).split(",");

        System.out.print("后缀式:");

        for(int i=0;i<s.length;i++){

            if(!s[i].equals(""))

                System.out.print(s[i]);

            }

        System.out.println("\n"+"结果:"+count(transform(st)));

        }

}

 

LinkStack.java

 

public class LinkStack<T>{

    private class Node{

        private T date;

        private Node next;

        public Node(){}

        public Node(T date,Node next){

            this.date=date;

            this.next=next;

            }

        }

    private Node top;

    private int size;

    public LinkStack(){

        top=null;

        }

    public LinkStack(T element){

        top=new Node(element,null);

        size++;

        }

    public int length(){

        return size;

        }

    public void push(T element){

        top=new Node(element,top);

        size++;

        }

    public boolean Empty(){

        return size==0;

        }

    public T peek(){

        return top.date;

        }

    public T pop(){

        Node oldTop=top;

        top=top.next;

        oldTop.next=null;

        size--;

        return oldTop.date;

        }

    public void clear(){

        top=null;

        size=0;

        }

    public String toString(){

        if(Empty()){

            return "[]";

            }

        else{

            StringBuffer sb=new StringBuffer("[");

            for(Node current=top;current!=null;current=current.next){

                sb.append(current.date.toString());

                if(current.next!=null){

                    sb.append(",");

                    }

            }

        return sb.append("]").toString();

        }

    }



}