老哥为何答案正确不了

Question

public class ExceptionTest { public static void main(String[] args) { Scanner sc=new Scanner(System.in); try { System.out.println("你的选择是:A,B,C,D"); String s=sc.next(); if(s=="a"){ System.out.println("选择正确"); } else{ System.out.println("选择错误"); } } catch (InputMismatchException e) { System.out.println("请重新输入"); } }}