regarding generics

[Deepthi Kanakam Rajan]

Hi,

This is one of the questions given in epracticelabs demo exam:

import java.util.*;

public class PayRoll
{

public static void main(String argv[])
{
Vector<String>employeeList = new Vector<String>();

Vector<Integer>employeeIdList = new Vector<Integer>();

Vector<Object>employeeProfileList = new Vector<Object>();

System.out.println(employeeList.getClass()==employeeIdList.getClass());
System.out.println(employeeList.equals(employeeProfileList);
System.out.println(employeeList.getClass()==employeeProfileList.getClass());
System.out.println(employeeIdList.equals(employeeProfileList);

}
}

the answer gven is false false false true.

teh reason given that all instances of a generic class have the same runtime class so getClass() returns java.util.Vector.

In that case, the answer should have been true true true true.

Appreciate a clarification on this.

Thanks in advance.

[Mateusz Kwasniewski]

Yes, I think you're right. The answer should be true true true true.

Vector<String> employeeList = new Vector<String>(); //at compile time
Vector employeeList = new Vector(); //at runtime

Each call to employeeList.getClass(),employeeIdList.getClass(),
employeeProfileList.getClass() returns class java.util.Vector so both
comparisions with == return true.

On the other hand, to find out why equals returns true in both cases you
should remember that List interface overrides equals. API says:

...two Lists are defined to be equal if they contain the same elements in the same order.

Since in our example the vectors are empty we get true twice.

Even if you have someting like:

ArrayList list = new ArrayList();
Vector<String>employeeList = new Vector<String>();
System.out.println(employeeList.equals(list)); //true

You will get true.

It's my first post here, so please correct me if I'm wrong