java实现两数运算为什么运行错误

    在eclipse 进行两个数的运算，为什么运行不了                       

把变量cha的类型改为String类型可能更适合

import java.util.Scanner;

public class Calculate {
    
    Integer num1,num2;
    String cha;
    Scanner num;
    String add="+", red="-",mul="*",rem="/";
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Calculate result = new Calculate();
        result.counter();
        
    }
    
    public void counter() {
        
        num = new Scanner(System.in);
        num1=num.nextInt();
        //System.out.println("num1="+num1);
        cha = num.next();
        
        num2=num.nextInt();
        //System.out.println("num2="+num2);
        
        
        
        
        if(cha.equals(add)) {
            System.out.println(num1+add+num2+"="+(num1+num2));
        }
        
        if(cha.equals(red)) {
            System.out.println(num1+red+num2+"="+(num1-num2));
        }
        
        if(cha.equals(mul)) {
            System.out.println(num1+mul+num2+"="+(num1*num2));
        }
        
        if(cha.equals(rem)) {
            System.out.println(num1+rem+num2+"="+(num1/num2));
        }
    }

}

报错信息截图贴一下。