代码如下：

public class Calculator {
    public static void main(String[] args) {
        String expression = "7*2-5*2";
        int length = expression.length();
        CalcuStack numStack = new CalcuStack(length);
        CalcuStack operStack = new CalcuStack(length);
        char[] chars = expression.toCharArray();
        String keepNum = "";
        int num1 = 0;
        int num2 = 0;
        int oper = 0;
        int res = 0;
        for (int i = 0; i < chars.length; i ++) {
            if (operStack.isOper(chars[i])) {
                operStack.list();
                if (!operStack.isEmpty()) {
                    if (operStack.priority(chars[i]) <= operStack.priority(operStack.peek())) {
                        num1 = numStack.pop();
                        num2 = numStack.pop();
                        oper = operStack.pop();
                        res = numStack.cal(num1, num2, oper);
                        numStack.push(res);
                        operStack.push(chars[i]);
                    } else {
                        operStack.push(chars[i]);
                    }
                } else {
                    operStack.push(chars[i]);
                }
            } else {
                int count = 0;
                for (int a = i; a + count < chars.length; count ++) {
                    if (operStack.isOper(chars[a + count])) {
                        i = i + count - 1;
                        break;
                    }
                    keepNum += chars[a + count];
                }
                numStack.push(Integer.parseInt(keepNum));
                keepNum = "";
            }
        }
        numStack.list();
        operStack.list();
        while (true) {
            if (operStack.isEmpty()) {
                break;
            }
            num1 = numStack.pop();
            num2 = numStack.pop();
            oper = operStack.pop();
            res = numStack.cal(num1, num2, oper);
            numStack.push(res);
        }

        int res2 = numStack.pop();
        System.out.printf("%s=%d\n", expression, res2);
    }
}

class CalcuStack {
    private int maxSize;
    private int[] stack;
    private int top = -1;
//    构造函数
    public CalcuStack(int maxSize) {
        this.maxSize = maxSize;
        this.stack = new int[maxSize];
    }
//    判断是否栈满
    public boolean isFull() {
        return top == maxSize - 1;
    }
//    判断是否栈空
    public boolean isEmpty() {
        return top == -1;
    }
//    获取栈顶数据,不出栈
    public int peek() {
        return stack[top];
    }
//    入栈
    public void push(int data) {
        if (isFull()) {
            System.out.println("栈满");
            return;
        }
        top ++;
        stack[top] = data;
    }
//    出栈
    public int pop() {
        if (isEmpty()) {
            throw new RuntimeException("栈空,无数据");
        }
        int value = stack[top];
        top --;
        return value;
    }
//    遍历栈
    public void list() {
        if (isEmpty()) {
            System.out.println("栈空,无数据");
            return;
        }
        for (int i = top; i >= 0; i --) {
            System.out.printf("stack[%d]=%d\n", i, stack[i]);
        }
    }
//    判断计算符优先级
    public int priority(int oper) {
        if (oper == '*' || oper == '/') {
            return 1;
        } else if (oper == '+' || oper == '-') {
            return 0;
        } else {
            return -1;
        }
    }
//    判断是否运算符
    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 = num1 / num2;
                break;
            default:
                break;
        }
        return res;
    }
}