import java.util.Scanner;public class Rectangle extends Shape { @Override public void zhouchang() { // TODO Auto-generated method stub System.out.println("請輸入長方形的長度："); int a=input.nextInt(); System.out.println("請輸入長方形的寬度："); int b=input.nextInt(); int num=a+b; System.out.println("長方形的周長為"+num); }報錯Exception in thread "main" java.lang.Error: Unresolved compilation problems:? input cannot be resolved為啥?。渴且驗椴皇莔ain方法？