Java实现简单的思维运算（只有加减乘除）

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
package cn.zhouyu.test;

import java.util.Stack;

public class EvaluateExpression {
	
	public static void main(String[] args) {
		String expression = "(1+2)*4-3";
		//1.1、创建一个存储操作数的栈
		Stack<Integer> operandStack = new Stack<>();
		//1.2、创建一个存储操作符和括号的栈
		Stack<Character> operatorStack = new Stack<>();
		//1.3、在expression的每个字符旁边插入空格，方便下面分割
		expression = insertBlanks(expression); 
		//1.4、分割expression，得到单个的操纵数、操作符和括号
		String[] tokens = expression.split(" ");
		
		for(String token : tokens) {
			//把分割后剩下的空格去掉
			if(token.length() == 0) {
				continue;
			}
			//2.1、如果是+或-操作符，处理在operatorStack栈顶的所有操作符。
			else if(token.charAt(0) == '+' || token.charAt(0) == '-') {
				while(!operatorStack.isEmpty() && 
					(operatorStack.peek()== '+'||
					operatorStack.peek()== '-'||
				  	operatorStack.peek()== '*'||
				   	operatorStack.peek()== '/')){
					//计算operandStack中的两个数的加减乘除
					processAnOperator(operandStack, operatorStack);
				}
				operatorStack.push(token.charAt(0));
			}
			//2.2、如果是*或/操作符，处理在operatorStack栈顶的所有*和/操作符
			else if(token.charAt(0) == '*' || token.charAt(0) == '/') {
				while(!operatorStack.isEmpty()&&
					(operatorStack.peek()== '*'||
				   	operatorStack.peek()== '/')) {
					processAnOperator(operandStack, operatorStack);
				}
				operatorStack.push(token.charAt(0));
			}
			//2.3、如果是(，压入operatorStack
			else if(token.charAt(0) == '(') {
				operatorStack.push('(');
			}
			//2.4、如果是)，重复处理来自operatorStack栈顶的操作符，直到看到栈上的(符号。
			else if(token.charAt(0) == ')') {
				while(operatorStack.peek()!='(') {
					processAnOperator(operandStack,operatorStack);
				}
				operatorStack.pop();
			}
			else {
				operandStack.push(new Integer(token));
			}
		}
		//清除栈：重复处理来自operatorStack栈顶的操作符，直到operatorStack为空为主
		while(!operatorStack.isEmpty()) {
			processAnOperator(operandStack,operatorStack);
		}
		
		System.out.println(operandStack.pop());
	}

	private static String insertBlanks(String expression) {
		String result = "";
		for(int i=0;i<expression.length();i++) {
			if(expression.charAt(i) == '(' || expression.charAt(i) == ')' || 
			   expression.charAt(i) == '+' || expression.charAt(i) == '-' ||
			   expression.charAt(i) == '*' || expression.charAt(i) == '/' ) {
				result += " " + expression.charAt(i) + " ";
			}else{
				result += expression.charAt(i);
			}
		}
		return result;
	}
	
	public static void processAnOperator(Stack<Integer> operandStack,Stack<Character> operatorStack) {
		char op = operatorStack.pop();
		int op1 = operandStack.pop();
		int op2 = operandStack.pop();
		//这里注意，别写成op1/op2。在expression中应该是op2/op1，因为op2先入栈
		if(op == '+') {
			operandStack.push(op2+op1);
		}
		else if(op == '-') {
			operandStack.push(op2-op1);
		}
		else if(op == '*') {
			operandStack.push(op2*op1);
		}
		else if(op == '/') {
			operandStack.push(op2/op1);
		}
		
	}
}