Call stack behavior in Java - Practice Problems & Coding Challenges

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Challenge - 5 Problems

💻 code output

intermediate

What is the output of this recursive call stack?

Consider the following Java code that uses recursion. What will be printed when countdown(3) is called?

Java

public class Test {
    public static void countdown(int n) {
        if (n == 0) {
            System.out.println("Done");
            return;
        }
        System.out.println(n);
        countdown(n - 1);
    }

    public static void main(String[] args) {
        countdown(3);
    }
}

A

Done
1
2
3

B

3
2
1
Done

C

3
2
1

D Done

💻 code output

intermediate

What is the value of variable after nested method calls?

Given the following Java code, what is the value of result after main finishes?

Java

public class Test {
    public static int addOne(int x) {
        return x + 1;
    }

    public static int doubleIt(int x) {
        return x * 2;
    }

    public static void main(String[] args) {
        int result = doubleIt(addOne(3));
        System.out.println(result);
    }
}

A 8

B 7

C 6

D 5

💻 code output

advanced

What is printed by this mutual recursion example?

Examine the following Java code with two mutually recursive methods. What is the output when foo(2) is called?

Java

public class Test {
    public static void foo(int n) {
        System.out.println("foo " + n);
        if (n == 0) {
            System.out.println("foo done");
            return;
        }
        bar(n - 1);
    }

    public static void bar(int n) {
        if (n == 0) {
            System.out.println("bar done");
            return;
        }
        System.out.println("bar " + n);
        foo(n / 2);
    }

    public static void main(String[] args) {
        foo(2);
    }
}

A

foo 2
bar 1
foo 0
bar done
foo done

B

foo 2
bar 1
foo 1
bar 0
bar done
foo done

C

foo 2
bar 1
foo 0
foo done

D

foo 2
bar 1
foo 1
bar 0
foo done
bar done

🔧 debug

advanced

What error does this recursive method cause?

Consider this Java method that calls itself without a base case. What error will occur when infiniteRecursion() is called?

Java

public class Test {
    public static void infiniteRecursion() {
        infiniteRecursion();
    }

    public static void main(String[] args) {
        infiniteRecursion();
    }
}

A No error, program runs forever

B NullPointerException

C IllegalArgumentException

D StackOverflowError

🧠 conceptual

expert

How many stack frames are created during this recursive factorial call?

Given the following factorial method, how many stack frames are created when factorial(5) is called?

Java

public class Test {
    public static int factorial(int n) {
        if (n <= 1) return 1;
        return n * factorial(n - 1);
    }

    public static void main(String[] args) {
        int result = factorial(5);
        System.out.println(result);
    }
}

A 6

B 5

C 4

D 1