Java MCQ Questions – Page 175 of 200

Q: What is the output of this code?

B) 6. The loop iterates for `i = 0, 1, 2`. It sums `numbers[0] (1) + numbers[1] (2) + numbers[2] (3)`, resulting in `1 + 2 + 3 = 6`.

Q: What compilation error will this Java code produce?

B) Error: duplicate default label. A switch statement can only have one default label. Having multiple default labels will result in a compilation error indicating a duplicate default.

Q: What is the output of this code?

A) Original: [10, 2] Clone: [10, 2, 30]. LinkedList's `clone()` performs a shallow copy. This means `original` and `clone` refer to the same `MutableInt` objects. Changing `clone.get(0).value` also changes `original.get(0).value`. However, `clone.add()` adds a new `MutableInt` object only to the `clone` list.

Q: What is the output of this Java code?

A) Producer trying to put 1 Consumer trying to take Producer put 1 Consumer took 1. A `SynchronousQueue` has zero capacity; a `put()` operation must wait for a `take()` operation, and vice-versa. The `Thread.sleep()` orchestrates the output by letting the producer try to put before the consumer tries to take, leading to a direct handoff.

Q: Can two methods be overloaded if they only differ by their return type?

B) No, this is not allowed.. Method overloading requires differences in the parameter list. Two methods with the same name and same parameter list, but different return types, will result in a compile-time error.

Q: What is wrong with this Java code?

A) Lambda expressions cannot be assigned directly to the `Object` type.. Lambda expressions require a target type that is a functional interface. `Object` is not a functional interface, so a lambda expression cannot be assigned to it directly without an explicit cast to a compatible functional interface.

Q: What is the output of this code?

B) 0 -1. `indexOf("apple")` returns the index of the first occurrence of 'apple', which is 0. `lastIndexOf("orange")` returns -1 because 'orange' is not present in the list. The output is '0 -1'.

Q: What is the output of this code?

A) A10B10B. The `new B()` call first invokes `B()` which chains to `this(10)`. `B(int x)` then chains to `super(x)`, printing 'A10'. After `super(x)` returns, `B(int x)` prints 'B10'. Finally, `B()` completes and prints 'B'.

Q: Which exception is thrown when the `main` method of this Java code is executed?

A) java.lang.NullPointerException. The `String(char[] value)` constructor expects a non-null character array. Passing `null` as the argument will cause a `NullPointerException` at runtime.

Q: Consider a `try-with-resources` block that attempts to close two custom resources, `ResourceA` and `ResourceB`, each of which might throw a distinct custom exception (`ResourceAException` and `ResourceBException` respectively) during their `close()` method. If both `ResourceA.close()` and the main `try` block body throw exceptions, what happens to `ResourceBException` (if thrown by `ResourceB.close()`)?

C) It is suppressed by the primary exception (from the `try` block or `ResourceA.close()`) and can be retrieved via `getSuppressed()`.. In `try-with-resources`, if an exception occurs in the main `try` block and another in a resource's `close()` method, the exception from `close()` is suppressed. The primary exception (from the `try` block or the first resource's `close()`) is thrown, and suppressed exceptions can be retrieved using `Throwable.getSuppressed()`.

Q3481 easy code output

What is the output of this code?

java

public class Test {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        int result = 0;
        for (int i = 0; i < 3; i++) {
            result += numbers[i];
        }
        System.out.println(result);
    }
}

Q3482 medium code error

What compilation error will this Java code produce?

java

public class SwitchError {
    public static void main(String[] args) {
        int day = 3;
        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            default:
                System.out.println("Weekend");
                break;
            default:
                System.out.println("Another default");
                break;
        }
    }
}

Q3483 hard code output

What is the output of this code?

java

import java.util.LinkedList;

public class Test {
    static class MutableInt {
        int value;
        MutableInt(int v) { this.value = v; }
        public String toString() { return String.valueOf(value); }
    }
    public static void main(String[] args) {
        LinkedList<MutableInt> original = new LinkedList<>();
        original.add(new MutableInt(1));
        original.add(new MutableInt(2));
        LinkedList<MutableInt> clone = (LinkedList<MutableInt>) original.clone();
        clone.get(0).value = 10; // Modifies content of shared MutableInt object
        clone.add(new MutableInt(30)); // Adds a new object to clone
        System.out.println("Original: " + original);
        System.out.println("Clone: " + clone);
    }
}

Q3484 hard code output

What is the output of this Java code?

java

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;

public class QueueTest {
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<Integer> sq = new SynchronousQueue<>();

        new Thread(() -> {
            try {
                System.out.println("Producer trying to put 1");
                sq.put(1);
                System.out.println("Producer put 1");
            } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
        }).start();

        Thread.sleep(100);

        new Thread(() -> {
            try {
                System.out.println("Consumer trying to take");
                Integer val = sq.take();
                System.out.println("Consumer took " + val);
            } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
        }).start();

        Thread.sleep(500);
    }
}

Q3485 easy

Can two methods be overloaded if they only differ by their return type?

Q3486 easy code error

What is wrong with this Java code?

java

public class Test {
    public static void main(String[] args) {
        Object obj = () -> System.out.println("Hello from lambda");
    }
}

Q3487 medium code output

What is the output of this code?

java

import java.util.LinkedList;

public class Test {
    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<>();
        list.add("apple");
        list.add("banana");
        list.add("apple");
        list.add("cherry");
        System.out.println(list.indexOf("apple") + " " + list.lastIndexOf("orange"));
    }
}

Q3488 hard code output

What is the output of this code?

java

class A {
    A() { System.out.print("A"); }
    A(int x) { System.out.print("A" + x); }
}
class B extends A {
    B() { this(10); System.out.print("B"); }
    B(int x) { super(x); System.out.print("B" + x); }
}
public class Main {
    public static void main(String[] args) {
        new B();
    }
}

Q3489 hard code error

Which exception is thrown when the `main` method of this Java code is executed?

java

public class CharArrayToStringNull {
    public static void main(String[] args) {
        char[] chars = null;
        try {
            String s = new String(chars);
            System.out.println(s);
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q3490 hard

Consider a `try-with-resources` block that attempts to close two custom resources, `ResourceA` and `ResourceB`, each of which might throw a distinct custom exception (`ResourceAException` and `ResourceBException` respectively) during their `close()` method. If both `ResourceA.close()` and the main `try` block body throw exceptions, what happens to `ResourceBException` (if thrown by `ResourceB.close()`)?

Q3491 easy code output

What does this Java code print?

java

public class WhileLoopDemo {
    public static void main(String[] args) {
        int i = 0;
        while (i < 5) {
            if (i == 2) {
                break;
            }
            System.out.print(i);
            i++;
        }
    }
}

Q3492 medium code error

What compile-time error will occur when the `Derived` class tries to override the `display()` method?

java

class Base {
    public final void display() {
        System.out.println("Base display method");
    }
}

class Derived extends Base {
    @Override
    public void display() {
        System.out.println("Derived display method");
    }
}

public class Main {
    public static void main(String[] args) {
        new Derived().display();
    }
}

Q3493 hard code error

Which exception is thrown when the `main` method of this Java code is executed?

java

public class StringRepeatNegativeCount {
    public static void main(String[] args) {
        String s = "abc";
        try {
            // String.repeat() is available from Java 11 onwards
            String repeated = s.repeat(-1);
            System.out.println(repeated);
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q3494 medium

After executing `Arrays.sort(myArray);` on an array of primitive integers, what is the guaranteed state of `myArray`?

Q3495 easy

Which Java primitive data type is used to store a single 16-bit Unicode character?

Q3496 easy code output

What does this code print?

java

import java.util.LinkedList;
import java.util.Queue;

public class Main {
    public static void main(String[] args) {
        Queue<Character> letters = new LinkedList<>();
        letters.offer('A');
        letters.offer('B');
        System.out.println(letters.poll());
        letters.add('C');
        System.out.println(letters.element());
    }
}

Q3497 hard

Consider an object used as a key in a `HashMap`. If the state of this key object changes *after* it has been inserted into the map, such that its `hashCode()` value is altered, what is the most likely outcome when attempting to retrieve the associated value using the *modified* key?

Q3498 medium

What is the average time complexity for accessing an element by its index using `get(int index)` in `java.util.LinkedList`?

Q3499 easy code output

What is the output of this code?

java

import java.util.function.Predicate;

public class LambdaTest {
    public static void printIf(int num, Predicate<Integer> condition) {
        if (condition.test(num)) {
            System.out.println(num);
        }
    }

    public static void main(String[] args) {
        printIf(7, n -> n > 5);
    }
}

Q3500 easy

After calling the `start()` method on a new thread, what state does it enter?

☕ Java MCQ Questions – Page 175