You need to store elements in a collection that guarantees that no duplicates are stored. Which two interfaces provide that capability？（）   

switch （i）  { 
default： 
System.out.printIn（“Hello”）； 
} 
What is the acceptable type for the variable i？（）  

1. int I=1， j=0 
2.   
3. switch（i）  { 
4. case 2： 
5. j+=6； 
6.   
7. case 4： 
8. j+=1； 
9.   
10. default： 
11. j +=2； 
12.   
13. case 0： 
14. j +=4； 
15. } 
16.     
What is the value of j at line 16？（）

public class WhileFoo { 
public static void main （String []args）   { 
int x= 1， y = 6； 
while （y--）  {x--；} 
system.out.printIn（“x=” + x “y =” + y）； 
} 
}  
What is the result？（）