求大神解答，为啥报错

Question

import java.util.Scanner;public class Rectangle extends Shape { @Override public void zhouchang() { // TODO Auto-generated method stub System.out.println("请输入长方形的长度："); int a=input.nextInt(); System.out.println("请输入长方形的宽度："); int b=input.nextInt(); int num=a+b; System.out.println("长方形的周长为"+num); }报错Exception in thread "main" java.lang.Error: Unresolved compilation problems:  input cannot be resolved为啥啊？是因为不是main方法？