What is my error in using a String in the case method

I am very new and young and i can not see what the error is. I am trying to use the Scanner to hold a String for how how and if how =yes execute the yes case and if no execute the no case this is all inside the else statement from the first question

package test;
import java.util.Scanner;
public class Try {
public static void main(String[] args) {
System.out.println("hello world");
 Scanner input = new Scanner(System.in);
 System.out.println("Do you wanna make android apps");
 System.out.println("Yes or no ?");
 String copy=input.nextLine();
 System.out.println(copy);
 if(copy.equals("yes")){
     System.out.println("you should continue java");





 }else{

 System.out.println("Do you wanna make iso apps");
 System.out.println("yes or no");
 String how = null;
 switch(how.toLowerCase()){

 case "yes" :System.out.println("test worked");
 break;
 case "no":System.out.println("test worked 2");
 break;


 }


  }
 }}