栈实现计算器

public static void main(String[] args) {
         //完成表达式运算
        String s="30+2*5-6+7";
        //创建两个栈 一个数栈 一个符号栈
        ArrayStack arrayStack=new ArrayStack(10);
        ArrayStack arrayStack1=new ArrayStack(10);

        int index=0;
        int num1=0;
        int num2=0;
        int oper=0;
        int res=0;
        char ch=' ';
        String keepnum="";
        while (true)
        {
            //依次得到s中的每一个字符
            ch=s.charAt(index);

            if(!arrayStack.isOper(ch))
            {
                keepnum+=ch;
                if(index==s.length()-1)
                arrayStack.push(ch-48);
                else
                {
                    if(arrayStack.isOper(s.charAt(index+1)))
                    {
                        arrayStack.push(Integer.parseInt(keepnum));
                        System.out.println(keepnum);
                        keepnum="";

                    }
                }

            }
            else if(arrayStack.isOper(ch))
            {
                if(arrayStack1.isEmpty())
                {
                    arrayStack1.push(ch);
                }
              else   if(arrayStack.priority(ch)<=arrayStack.priority(arrayStack1.peek()))
                {

                    num1=arrayStack.pop();
                    num2=arrayStack.pop();
                    oper=arrayStack1.pop();
                    res=arrayStack.cal(num1,num2,oper);
                    arrayStack.push(res);
                    arrayStack1.push(ch);
                }
                else
                {
                    arrayStack1.push(ch);
                }
            }
            if(index==s.length()-1)
            {
                break;
            }
            index++;
        }
        while (!arrayStack1.isEmpty())
        {
            num1=arrayStack.pop();
            num2=arrayStack.pop();
            oper=arrayStack1.pop();
            res=arrayStack.cal(num1,num2,oper);
           arrayStack.push(res);
        }
        System.out.println(arrayStack.pop());
    }
}
//定义一个栈 增加一些功能
class ArrayStack
{
    private  int maxSize;
    private  int[]stack;
    private  int top=-1;
    public ArrayStack(int maxSize)
    {
        this.maxSize=maxSize;
        stack=new int[this.maxSize];

    }
    //判断栈满
    public  boolean isFull()
    {
        return  top==maxSize-1;
    }
    //判断栈空
    public  boolean isEmpty()
    {
        return  top==-1;
    }
    //入栈
    public  void push(int val)
    {
        if( isFull()) return;
        top++;
        stack[top]=val;
    }
    //出栈
    public int pop()
    {
        if(isEmpty()) return -1;
        int val=stack[top];
        top--;
        return   val;

    }
    //显示栈顶
    public int peek()
    {
        if(isEmpty()) return -1;
        int val=stack[top];
        return   val;

    }
    //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 int priority(int oper)
    {
        if(oper=='*'||oper=='/') return 1;
        else if(oper=='+'||oper=='-') return 0;
        else
        {
            return -1; //假定目前表达式只有+ - * /
        }
    }
    //判断是否是一个运算符
    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 = num2 / num1;
                break;
            case '*':
                res = num1 * num2;
            default:
                break;
        }
        return  res;
    }