java简单实现中缀转后缀

缺点：目前只实现10之内的四则运算

学到的知识点：

StringBuffer若是想转char数组，首先转String,而后装Char

String tem1=st.toString();

    char tem[]=tem1.toCharArray();

如何将字符转数字Float要使用包装类型

Float.valueOf(tem[i]-'0')

import java.nio.CharBuffer;

import java.util.Stack;

public class ZhongZhui {

static Stack<Character> stack = new Stack();

public static void main(String[] args) {

 String s="5+2*(3*(2-1))";
 
 StringBuilder out1=getLast(s);
 
   float result= calsum(out1);
   
    System.out.println(result);
	
}
public static float getSum(char op,float n1,float n2){

    if(op=='+')
	
        return n1+n2;
		
    if(op=='-')
	
        return n2-n1;
		
    if(op=='*')
	
        return n1*n2;
		
    if(op=='/')
	
        return n2/n1;
		
    return 0;
}

public static float calsum(StringBuilder st){

    Stack<Float> sum = new Stack();
	
    String tem1=st.toString();
	
    char tem[]=tem1.toCharArray();
	
    for(int i=0;i<tem.length;i++){
	
        if(tem[i]>='0'&&tem[i]<='9'){
		
            System.out.println("temp"+tem[i]);
			
            sum.push(Float.valueOf(tem[i]-'0'));
			
        }else {
		
            float t=getSum(tem[i],sum.pop(),sum.pop());
			
            System.out.println("t"+t);
			
            sum.push(t);
        }
    }
    
    return sum.pop();
}
public static StringBuilder getLast(String s){

   char st[]=s.toCharArray();
   
    StringBuilder out =new StringBuilder();
	
    for(int i=0;i<st.length;i++){
	
        char temp =st[i];
		
        if(temp==' ')
		
            continue;
			
        //若是是数字，添加到输出字符串
		
         if(temp>='0'&&temp<='9'){
		 
             System.out.println("hell0");
			 
             out.append(temp);
			 
             continue;
         }
		 
         //若是碰到的是左括号，压入栈中
		 
         if(temp=='('){
		 
             stack.push(temp);
			 
             System.out.println("hello(");
			 
             continue;
         }

         //若是符号是+或者-，当符号栈非空而且栈定元素不为（，
		 
        //则将栈顶符号出栈，重复上述步骤，直到while循环不成立，退出，而后把符号压入
		
        //理解也很简单，由于+-的优先级最低，因此符号栈的符号只要不遇到
		
        //左括号就出栈

        if(temp=='+'||temp=='-'){
		
            while((!stack.empty())&&(stack.peek()!='(')){
			
                System.out.println("jia");
				
                out.append(stack.pop());
				
            }
			
            stack.push(temp);
			
            continue;
        }
		
        //如何遇到右括号，将左括号以后的元素都出栈输出，将左括号出栈不输出
		
       if(temp==')'){
	   
           while((!stack.empty())&&(stack.peek()!='(')){
		   
               System.out.println("you");
			   
               out.append(stack.pop());
			   
           }
		   
           stack.pop();
		   
           continue;
       }
	   
       //如遇到* /将符号栈的* /出栈并输出
	   
       if(temp=='*'||temp=='/'){
	   
           while ((!stack.empty())&&(stack.peek()=='*'||stack.peek()=='/')){
		   
               System.out.println("cheng");
			   
               out.append(stack.pop());
           }
		   
           stack.push(temp);
		   
           continue;
		   
       }
    }
    //字符串遍历完，再检查符号栈，将其中的都输出
	
    while (!(stack.empty())) {
	
        System.out.println("last");
		
        out.append(stack.pop());
		
    }
	
    return out;
}

}