思路

变量

String[] arr

Stack

代码

public class Test1 {
	public static void main(String[] args) {
		String s = "3 40 + 5 * 6 -";
		Stack numArr = new Stack(10);
		int num1 = 0;
		int num2 = 0;
		int res = 0;
		int index = 0;
		String[] arr = s.split(" ");
		for(String e:arr) {
			System.out.print(e);
		}
		System.out.println();
		while(true) {
			if(index >= arr.length) {
				break;
			}
			if(arr[index].matches("\\d+")) {
				numArr.push(Integer.parseInt(arr[index]));
			}else {
				num1 = numArr.pop();
				num2 = numArr.pop();
				String c = arr[index];
				res = numArr.cal(num1,num2,c);
				numArr.push(res);
			}
			index++;
		}
		res = numArr.pop();
		System.out.println(res);
	}
}
class Stack{
	private int top = -1;
	private int[] arr;
	private int maxsize;
	
	public Stack(int nums) {
		arr = new int[nums];
		this.maxsize = nums;
	}
	
	//栈空
	public boolean isEmpty() {
		return this.top == -1;
	}
	
	//栈满
	public boolean isFull() {
		return this.top == this.maxsize - 1;
	}
	
	//压栈
	public void push(int val) {
		if(isFull()) {
			System.out.print("栈满！");
			return;
		}
		top++;
		arr[top] = val;
	}
	
	//弹栈
	public int pop() {
		if(isEmpty()) {
			System.out.print("栈空！");
			return -1;
		}
		int val = arr[top];
		top--;
		return val;	
	}
	
	
	public void show() {
		if(isEmpty()) {
			System.out.print("栈空！");
			return;
		}
		for(int i = top; i >= 0; i--) {
			System.out.println(arr[i]);
		}
	}
	
	//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
	public int prior(int i) {
		if(i == '+' || i == '-') {
			return 0;
		}else if(i == '*' || i == '/') {
			return 1;
		}else {
			return -1;
		}
	}
	
	//查看栈顶元素
	public int peak() {
		return  arr[top];
	}
	//运算符
	public boolean isOper(String c) {
		return c == "+" || c == "-" || c == "*" || c == "/";
	}
	//计算
	
	public int cal(int num1, int num2, String c) {
		int res = 0;
		switch(c) {
			case "+":
				res = num1 + num2;
				break;
			case "-":
				res = num2 - num1;
				break;
			case "*":
				res = num2 * num1;
				break;
			case "/":
				res = num2 / num1;
				break;
			default:
				break;
		}
		return res;
	}
}