Possible error OCJP Practice Exams, exam 3 question 28

[John Wintermute]

Hi all,

When I worked through this question, I ended up with five objects, but the answer says it's only four. It seems to me that one Banker, one Account and three Longs are created

class Account {Long acctNum, password;}

public class Banker {
	public static void main(String[] args) {
		new Banker().go();
	}
	
	void go() {
		Account a1 = new Account();
		a1.acctNum = new Long("1024"); // 1
		Account a2 = a1;
		Account a3 = a2;
		
		a3.password = a1.acctNum.longValue(); // 2
		a2.password = 4455L; // 3
		
	}
}

I ran the code through the debugger in Eclipse and, indeed, Long instances are created with different IDs at lines 1,2 and 3.

Would anyone care to comment on that?

Many thanks!
-john

[Thomas Kennedy]

You didn't post the exact question. If it asked you how many objects are created by the whole program that's one thing, but if it asked how many are created between certain lines that's another.

I'm going to examine how many are created just within the go() method.

class Account {Long acctNum, password;}   
  
public class Banker {   
    public static void main(String[] args) {   
        new Banker().go();   
    }   
       
    void go() {   
        Account a1 = new Account();  // here's one
        a1.acctNum = new Long("1024"); // and another
        Account a2 = a1;
        Account a3 = a2; 
           
        a3.password = a1.acctNum.longValue(); // longValue returns a wrapper, which we assign to the reference variable, so that's one
        a2.password = 4455L; // and here's another wrapper, that makes four
    }   
}

I think the supplied answer, four objects, is correct if they meant just the doings within the go() method.

[John Wintermute]

Hi Thomas,

Yes, you are indeed correct - it's how many are eligible when the method ends. Another case of "read the question properly"

thanks!

john

[Jagat Sastry]

John, I think you're right. The question asks "When line 8 is reached, which are true?"

When line 8 is reached, you have those 4 objects mentioned by Thomas, plus the Banker object created in line 7 that would be eligible for GC.
That makes it five objects eligible for GC, right?

[An Tran]

Yes, it's 5 and was confirmed by the author here http://www.coderanch.com/t/531928/java-programmer-SCJP/certification/Garbage-Collection-found-OCP-Java