#9 most askedVery commonMediumJVM & memory

Stack vs heap, and how garbage collection works

New to JVM & memory? Learn it from scratch first
Memory: The Stack, the Heap & References →

🏢 Asked in real interviews

No reports yet. Were you asked this? Be the first to say where.

Where do variables and objects live in Java memory, and how does the garbage collector decide what to free?

🔮 Predict the output

public class Main {
    static void grow(int[] arr, int n) {
        n = n + 1;      // changes the local copy only
        arr[0] = 99;    // changes the shared object on the heap
    }
    public static void main(String[] args) {
        int n = 1;
        int[] arr = {1};
        grow(arr, n);
        System.out.println(n + " " + arr[0]);
    }
}

🎤 Answer it out loud, then check yourself

Say your answer as if the interviewer is listening (30–90 seconds). Then reveal what a strong answer covers and tick what you said.

Answer out loud first, then compare.

Want to rehearse it?
Answer this to the AI interviewer and get a verdict →