Garbage collection overview in Java - Practice Problems & Coding Challenges

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Challenge - 5 Problems

🧠 conceptual

intermediate

What is the primary purpose of garbage collection in Java?

Choose the best description of what garbage collection does in Java.

A Prevents the creation of new objects to save memory.

B Manually deletes objects when the programmer calls a delete method.

C Automatically frees memory by removing objects that are no longer reachable.

D Optimizes CPU usage by pausing all running threads.

❓ query result

intermediate

What output does this code produce regarding object finalization?

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

Java

class Test {
  protected void finalize() {
    System.out.println("Finalized");
  }
  public static void main(String[] args) {
    Test t = new Test();
    t = null;
    System.gc();
    System.out.println("End of main");
  }
}

A End of main

B

Finalized
End of main

C

End of main
Finalized

D No output

📝 syntax

advanced

Identify the syntax error in this garbage collection related code snippet

Which option contains a syntax error preventing compilation?

Java

public class GCExample {
  public static void main(String[] args) {
    Object obj = new Object();
    obj = null;
    System.gc();
  }
}

A finalize() { System.out.println("Cleaning up"); }

B protected void finalize() { System.out.println("Cleaning up"); }

C void finalize() { System.out.println("Cleaning up"); }

D public void finalize() { System.out.println("Cleaning up"); }

❓ optimization

advanced

Which approach helps reduce garbage collection overhead in Java?

Select the best practice to minimize the impact of garbage collection on application performance.

A Create many short-lived objects frequently to keep memory usage high.

B Avoid using local variables to reduce memory allocation.

C Call System.gc() explicitly after every object creation.

D Reuse objects when possible instead of creating new ones repeatedly.

🔧 debug

expert

Why does this Java program cause a memory leak despite garbage collection?

Examine the code below and select the reason it causes a memory leak.

Java

import java.util.ArrayList;
public class LeakExample {
  static ArrayList<Object> list = new ArrayList<>();
  public static void main(String[] args) {
    while(true) {
      Object obj = new Object();
      list.add(obj);
    }
  }
}

A The infinite loop causes the program to crash before garbage collection can run.

B Objects are never dereferenced because they are stored in a static list, preventing garbage collection.

C System.gc() is not called, so garbage collection never happens.

D The Object class does not support garbage collection.