• 栈实现综合计算器


    package com.dai.stack;
    
    public class Calculator {
    
        public static void main(String[] args) {
            //完成表达式的运算
            String expression = "103+2*6-6-6";
            //创建数栈和符号栈
            ArrayStack2 numStack = new ArrayStack2(10);
            ArrayStack2 operStack = new ArrayStack2(10);
            int index = 0; 
            int num1 = 0;
            int num2 = 0;
            int oper = 0;
            int res = 0;
            char ch = ' ';
            String keepNum = ""; //拼接多位数
            //开始用while循环扫描expression
            while(true) {
                ch = expression.substring(index, index+1).charAt(0);
                //判断ch是什么,再做相应处理
                if(operStack.isOper(ch)) {
                    //判断当前符号栈是否空
                    if(!operStack.isEmpty()) {
                        if(operStack.priority(ch) <= operStack.priority(operStack.peek())) {
                            num1 = numStack.pop();
                            num2 = numStack.pop();
                            oper = operStack.pop();
                            res = numStack.cal(num1, num2, oper);
                            //运算结果入数栈
                            numStack.push(res);
                            //当前操作符入符号栈
                            operStack.push(ch);
                        }
                        else {
                            operStack.push(ch);
                        }
                    }else {
                        operStack.push(ch);
                    }
                }
                else {
                    //处理多位数时,不能直接入栈,向右看一位是否为符号
                    keepNum += ch;
                    if(index == expression.length()-1) {
                        numStack.push(Integer.parseInt(keepNum));
                    }else {
                        
                    
                        if(operStack.isOper(expression.substring(index+1, index+2).charAt(0))) {
                            numStack.push(Integer.parseInt(keepNum));
                            keepNum = "";
                        }
                    }
                }
                //index +1 是否扫描到最后
                index++;
                if(index>=expression.length()) {
                    break;
                }
            }
            while(true) {
                //如果符号栈为空,则计算到最后的结果,数栈中只有一个数字
                if(operStack.isEmpty()) {
                    break;
                }
                num1 = numStack.pop();
                num2 = numStack.pop();
                oper = operStack.pop();
                res = numStack.cal(num1, num2, oper);
                numStack.push(res);
            }
            
            System.out.printf("表达式%s = %d
    ", expression, numStack.pop());
        }
    
    }
    
    //先创建一个栈
    class ArrayStack2{
        private int maxSzie;
        private int[] stack; //数组模拟栈,数据放在这
        private int top = -1; //表示栈顶,初始化为-1
        
        public ArrayStack2(int maxSize) {
            this.maxSzie = maxSize;
            stack = new int[this.maxSzie];
        }
        //栈满
        public boolean isFull() {
            return top==maxSzie-1;
        }
        //栈空
        public boolean isEmpty() {
            return top == -1;
        }
        //入栈 - push
        public void push(int value) {
            if(isFull()) {
                System.out.println("栈满了");
                return;
            }
            top++;
            stack[top] = value;
        }
        //出栈
        public int pop() {
            if(isEmpty()) {
                throw new RuntimeException("栈空,无数据");
            }
            int value = stack[top];
            top--;
            return value;
        }
        //返回栈顶元素
        public int peek() {
            return stack[top];
        }
        //遍历栈,遍历时需要从栈顶开始显示数据
        public void list() {
            if(isEmpty()) {
                System.out.println("栈空,没有数据");
                return;  
            }
            for(int i=top; i>=0; i--) {
                System.out.printf("stack[%d] = %d
    ", i, stack[i]);
            }
        }
        //优先级
        public int priority(int oper) {
            if(oper=='*'||oper=='/')
                return 1;
            if(oper=='+' || oper=='-')
                return 0;
            else 
                return -1;
        }
        //判断是不是运算符
        public boolean isOper(char val) {
            return val=='+'||val=='-'||val=='*'||val=='/';
        }
        
        //计算方法
        public int cal(int num1, int num2, int oper) {
            int res = 0;
            switch (oper) {
            case '+':
                res=  num1+num2;
                break;
            case '-':
                res = num2-num1;
                break;
            case '*':
                res = num1*num2;
                break;
            case '/':
                res = num2/num1;
                break;
            default:
                break;
            }
            return res;
        }
    
    }
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  • 原文地址:https://www.cnblogs.com/shengtudai/p/14364381.html
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