数据结构-Stack：施用栈来实现一个简易的算术表达式计算器

package org.cgz.practice;

import java.util.Stack;
import java.util.StringTokenizer;

class Caculator {
	
	/**
	 * 计算算术表达式的结果
	 * @param expression	表达式字符串
	 * @return
	 */
	public static double caculate(String expression) {
		//存储操作数的栈
		Stack<Double> operandStack = new Stack<Double>();
		//存储操作符的栈
		Stack<Character> operatorStack = new Stack<Character>();
		//拆分表达式
		StringTokenizer tokens = new StringTokenizer(expression, "()+-/*", true);
		while(tokens.hasMoreTokens()) {
			String token = tokens.nextToken().trim();
			if(token.length()==0) {
				continue;
			}else if(token.charAt(0)=='+' || token.charAt(0)=='-') {	
				//+或-的优先级比较低,因此需要计算前面所有的表达式
				while(!operatorStack.isEmpty() && 
					 (operatorStack.peek()=='+' || 
					  operatorStack.peek()=='-' || 
					  operatorStack.peek()=='*' || 
					  operatorStack.peek()=='/')) {
					processAnOperator(operandStack,operatorStack);
				}
				operatorStack.push(token.charAt(0));
			}else if(token.charAt(0)=='*' || token.charAt(0)=='/') {	
				//*或/优先级较高,需要看下一个操作符才能进行计算
				operatorStack.push(token.charAt(0));
			}else if(token.trim().charAt(0)=='(') {
				operatorStack.push('(');
			}else if(token.trim().charAt(0) == ')') {
				//计算()中的表达式的值				
				while(operatorStack.peek() != '(') {
					processAnOperator(operandStack,operatorStack);
				}
				//弹出'('
				operatorStack.pop();
			}else {
				//将操作数入栈
				operandStack.push(new Double(token));
			}
		}
		//计算剩下的表达式的结果
		while(!operatorStack.isEmpty()) {
			processAnOperator(operandStack, operatorStack);
		}
		//返回最后的结果
		return operandStack.pop();
	}
	
	/**
	 * 取出栈中的操作数和操作符 进行计算,并将结果push到operandStack
	 * @param operandStack
	 * @param operatorStack
	 */
	private static void processAnOperator(Stack<Double> operandStack,Stack<Character> operatorStack) {
		char op = operatorStack.pop();
		double op1 = operandStack.pop();
		double op2 = operandStack.pop();
		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);
		}
	}
}

public class CaculatorTest {
	public static void main(String[] args) {
		System.out.println(Caculator.caculate("3+2*(5+6/2)"));
	}
}

 计算结果：

19.0