中缀表达式计算（java）

/**
 * 数组表示栈
 */
public class CalArrayStack {
    //栈的大小
    private int maxSize;
    //数组
    private int[] stack;
    //    栈顶
    private int top = -1;
 
    public CalArrayStack(int maxSize) {
        this.maxSize = maxSize;
        stack = new int[maxSize];
    }
 
    //    栈满
    public boolean isFull() {
        return top == maxSize - 1;
    }
 
    //    栈空
    public boolean isEmpty() {
        return top == -1;
    }
 
    public void push(int num) {
        if (isFull()) {
            return;
        }
        top++;
        stack[top] = num;
    }
 
    public int pop() {
        if (isEmpty()) {
            throw new RuntimeException("栈数据为空");
        }
        int res = stack[top];
        top--;
        return res;
    }
 
    public int peek() {
        return stack[top];
    }
 
    //遍历栈
    public void list() {
        if (isEmpty()) {
            return;
        }
        for (int i = top; i >= 0; i--) {
            System.out.println(stack[i]);
        }
    }
 
    /**
     * 返回运算符的优先级，优先级使用数字表示
     * 数字越大，优先级越高；
     */
    public static int priority(int oper) {
        if (oper == '*' || oper == '/') {
            return 1;
        } else if (oper == '+' || oper == '-') {
            return 0;
        } else {
            return -1;
        }
    }
 
    //    判断是不是一个运算符
    public static boolean isOper(char val) {
        return val == '*' || val == '/' || val == '+' || val == '-';
    }
 
    //计算方法
    public static 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;
    }
}

public class Calculator {
    public static void main(String[] args) {
        //初始化表达式
        String expression = "7*2*2-5+1-5+3-4";
        int num = getCal(expression);
        System.out.println(num);
    }
 
    private static int getCal(String expression) {
        //    创建数字栈
        CalArrayStack numStack = new CalArrayStack(10);
        //    创建操作符栈
        CalArrayStack operStack = new CalArrayStack(10);
        //    定义需要的变量
        int index = 0;
        int num1 = 0;
        int num2 = 0;
        int oper = 0;
        int res = 0;
        String keepNum = "";
        //将每次扫描到的插入保存到ch
        char ch = ' ';
        //    开始遍历表达式
        while (true) {
            ch = expression.charAt(index);
            boolean isOper = CalArrayStack.isOper(ch);
            if (isOper) {
                if (operStack.isEmpty()) {
                    operStack.push(ch);
                } else {
                    int peek = operStack.peek();
                    if (CalArrayStack.priority(ch) > CalArrayStack.priority(peek)) {
                        operStack.push(ch);
                    } else {
                        num1 = numStack.pop();
                        num2 = numStack.pop();
                        oper = operStack.pop();
                        res = CalArrayStack.cal(num1, num2, oper);
                        numStack.push(res);
                        operStack.push(ch);
                    }
                }
            } else {
                keepNum += ch;
                //处理多位数
                while ((index + 1) < expression.length()) {
                    ch = expression.charAt(index + 1);
                    if (!CalArrayStack.isOper(ch)) {
                        index++;
                        keepNum += ch;
                    } else {
                        break;
                    }
                }
                numStack.push(Integer.valueOf(keepNum.toString()));
                keepNum = "";
            }
            index++;
            if (index == expression.length()) {
                break;
            }
        }
        while (!operStack.isEmpty()) {
            num1 = numStack.pop();
            num2 = numStack.pop();
            oper = operStack.pop();
            res = CalArrayStack.cal(num1, num2, oper);
            numStack.push(res);
        }
        return numStack.pop();
    }
}