trophyChallenge - 5 Problems

🎖️

Object Lifetime Master

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Test your skills under time pressure!

💻 code output

intermediate

2:00remaining

What is the output of this Java code involving object references?

Consider the following Java code snippet. What will be printed when it runs?

Java

class Box {
    int value;
    Box(int v) { value = v; }
}

public class Main {
    public static void main(String[] args) {
        Box b1 = new Box(10);
        Box b2 = b1;
        b2.value = 20;
        System.out.println(b1.value);
    }
}

A10

BCompilation error

C20

Attempts:

2 left

💻 code output

intermediate

2:00remaining

What happens to the object after null assignment?

What will be the output of this Java program?

Java

public class Main {
    public static void main(String[] args) {
        String s = new String("hello");
        s = null;
        System.out.println(s);
    }
}

Ahello

BRuntime NullPointerException

CCompilation error

Dnull

Attempts:

2 left

💻 code output

advanced

2:00remaining

What is the output when an object is eligible for garbage collection?

Consider this Java code. What will be printed?

Java

class Demo {
    protected void finalize() {
        System.out.println("Finalize called");
    }
}

public class Main {
    public static void main(String[] args) {
        Demo d = new Demo();
        d = null;
        System.gc();
        System.out.println("End of main");
    }
}

AEnd of main

BCompilation error

CFinalize called\nEnd of main

DRuntime error

Attempts:

2 left

🔧 debug

advanced

2:00remaining

Identify the error related to object lifetime and references

What error will this Java code produce when compiled or run?

Java

public class Main {
    public static void main(String[] args) {
        String s;
        System.out.println(s);
    }
}

ARuntime NullPointerException

BCompilation error: variable s might not have been initialized

CPrints null

DCompilation error: cannot find symbol s

Attempts:

2 left

🧠 conceptual

expert

2:00remaining

How many objects are eligible for garbage collection after this code?

Given the following code, how many objects are eligible for garbage collection immediately after line 10?

1: class Node {
2:   Node next;
3:   Node() { next = null; }
4: }
5: 
6: Node a = new Node();
7: Node b = new Node();
8: a.next = b;
9: b = null;
10: a = null;

Attempts:

2 left