Java MCQ Questions – Page 28 of 200

Q: If you want to create a custom exception that callers are *required* to handle or declare, which class should it extend?

C) java.lang.Exception. Extending `java.lang.Exception` (and not `RuntimeException`) makes a custom exception a checked exception, which mandates handling or declaration.

Q: What is the compilation issue in this Java code where method overloading is attempted using only different parameter names?

A) Compile-time error: Method 'combine(int, int)' is already defined in 'OverloadChecker'.. Method overloading depends on the number, types, and order of parameters, not on their names. Since both methods have the same name and parameter types in the same order, changing only the parameter names results in a duplicate method definition.

Q: What is the output of this code?

A) Modified. Both `obj` and `obj2` refer to the same mutable `MyMutableClass` object in memory. When `obj.setValue("Modified")` is called, it changes the state of that single object. Therefore, accessing the value through `obj2` will reflect the latest change.

Q: What is the output of this code?

B) null. If the specified key is not found in the HashMap, the `get` method returns `null`. 'Sarah' was never added as a key.

Q: What is the output of this code?

A) Hello World!. The append() methods of BufferedWriter return the BufferedWriter instance itself, allowing method chaining. The final write("!") call is then executed on the BufferedWriter, appending the exclamation mark. All operations succeed and are flushed by close().

Q: What compilation error will occur in the `ResourceManager` class?

A) Unhandled exception: ResourceNotFoundException.. The `findResource` method declares `throws ResourceNotFoundException` (a checked exception). The `processResource` method calls `findResource` but neither catches the `ResourceNotFoundException` nor declares `throws ResourceNotFoundException` itself, leading to a compile-time error.

Q: What error will be thrown when the `main` method tries to submit the second task after calling `executor.shutdownNow()`?

C) java.util.concurrent.RejectedExecutionException. Once an `ExecutorService` has been shut down (either with `shutdown()` or `shutdownNow()`), it will reject any new tasks submitted to it. This rejection manifests as a `java.util.concurrent.RejectedExecutionException`.

Q: Which of the following statements accurately describes an intermediate operation in the Java Stream API?

D) It transforms a stream into another stream, enabling chaining of operations.. Intermediate operations are designed to be chained; they take a stream as input and return a new stream, allowing multiple transformations to be applied sequentially.

Q: In an inheritance relationship, what is the class that is being inherited from called?

C) Superclass. The class from which another class inherits is known as the superclass, base class, or parent class.

Q: Given the interface `Predicate ` (which has `boolean test(String s)`), consider the following methods: java class StringUtils { public static boolean isPalindrome(String s) { return new StringBuilder(s).reverse().toString().equals(s); } public boolean containsVowel(String s) { return s.toLowerCase().matches(".*[aeiou].*"); } } Which of the following method references correctly instantiates a `Predicate `?

C) Predicate p3 = StringUtils::isPalindrome;. `StringUtils::isPalindrome` refers to a static method `isPalindrome(String s)` that matches the signature of `Predicate `'s `boolean test(String s)` method. Option B is an instance method and requires an object instance, or a different functional interface type (e.g., `BiPredicate `).

Q541 easy

If you want to create a custom exception that callers are *required* to handle or declare, which class should it extend?

Q542 medium code error

What is the compilation issue in this Java code where method overloading is attempted using only different parameter names?

java

public class OverloadChecker {
    public void combine(int num1, int num2) {
        System.out.println("Combination 1: " + (num1 + num2));
    }

    public void combine(int x, int y) { // This line causes the error
        System.out.println("Combination 2: " + (x * y));
    }

    public static void main(String[] args) {
        OverloadChecker oc = new OverloadChecker();
        oc.combine(5, 10);
    }
}

Q543 medium code output

What is the output of this code?

java

class MyMutableClass {
    private String value;

    public MyMutableClass(String value) {
        this.value = value;
    }

    public String getValue() { return value; }
    public void setValue(String value) { this.value = value; }
}

public class TestMutable {
    public static void main(String[] args) {
        MyMutableClass obj = new MyMutableClass("Initial");
        MyMutableClass obj2 = obj;
        obj.setValue("Modified");
        System.out.println(obj2.getValue());
    }
}

Q544 easy code output

What is the output of this code?

java

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> scores = new HashMap<>();
        scores.put("John", 90);
        scores.put("Mike", 85);
        System.out.println(scores.get("Sarah"));
    }
}

Q545 hard code output

What is the output of this code?

java

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.StringWriter;

public class Test {
    public static void main(String[] args) throws IOException {
        StringWriter sw = new StringWriter();
        BufferedWriter bw = new BufferedWriter(sw);
        bw.append("Hello ").append("World").write("!");
        bw.close();
        System.out.println(sw.toString());
    }
}

Q546 medium code error

What compilation error will occur in the `ResourceManager` class?

java

public class ResourceNotFoundException extends Exception {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}

public class ResourceManager {
    public String findResource(String id) throws ResourceNotFoundException {
        if (id.equals("invalid")) {
            throw new ResourceNotFoundException("Resource with ID " + id + " not found.");
        }
        return "Resource data for " + id;
    }

    public void processResource(String id) {
        String data = findResource(id);
        System.out.println("Processed: " + data);
    }

    public static void main(String[] args) {
        ResourceManager manager = new ResourceManager();
        manager.processResource("invalid");
    }
}

Q547 hard code error

What error will be thrown when the `main` method tries to submit the second task after calling `executor.shutdownNow()`?

java

import java.util.concurrent.*;

public class ExecutorShutdown {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(1);

        executor.submit(() -> System.out.println("Task 1 executed"));

        executor.shutdownNow(); // Immediately shuts down the executor

        try {
            // Attempt to submit a new task after shutdown
            executor.submit(() -> System.out.println("Task 2 executed"));
        } catch (RejectedExecutionException e) {
            System.err.println("Caught: " + e.getClass().getName());
        }
    }
}

Q548 medium

Which of the following statements accurately describes an intermediate operation in the Java Stream API?

Q549 easy

In an inheritance relationship, what is the class that is being inherited from called?

Q550 hard

Given the interface `Predicate<String>` (which has `boolean test(String s)`), consider the following methods: java class StringUtils { public static boolean isPalindrome(String s) { return new StringBuilder(s).reverse().toString().equals(s); } public boolean containsVowel(String s) { return s.toLowerCase().matches(".*[aeiou].*"); } } Which of the following method references correctly instantiates a `Predicate<String>`?

Q551 medium code error

What error occurs when running this Java code?

java

public class MyClass {
    public static void main(String[] args) {
        StringBuffer sb = null;
        sb.append("Hello");
        System.out.println(sb);
    }
}

Q552 medium

Consider the following Java generic method signature: `public static void processList(List<? extends Number> list)`. Which types of lists can be passed to this method?

Q553 medium

How can you create an effectively immutable `List` in Java 9+ that explicitly prevents any subsequent modifications?

Q554 hard

`java.util.concurrent.TransferQueue` extends `BlockingQueue` and introduces a unique method `transfer(E e)`. What is the primary semantic difference of `transfer(E e)` compared to `put(E e)`?

Q555 hard

What is the primary benefit of immutability in a multi-threaded environment beyond simply preventing data corruption (race conditions)?

Q556 easy code output

What does this code print?

java

import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<Integer> numbers = new LinkedList<>();
        numbers.add(10);
        numbers.addFirst(5);
        numbers.addLast(20);
        System.out.println(numbers);
    }
}

Q557 easy code error

What is the expected error when compiling and running the following Java code?

java

import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<>();
        list.add("One");
        String item = list.get(1); // Accessing index 1
    }
}

Q558 medium

Which type of method reference can be used to refer to a static method of a class?

Q559 hard code output

What is the output of this Java code?

java

import java.util.PriorityQueue;
import java.util.Comparator;

class MyInt {
    int value;
    MyInt(int v) { this.value = v; }
    @Override public String toString() { return String.valueOf(value); }
}

public class QueueTest {
    public static void main(String[] args) {
        PriorityQueue<MyInt> pq = new PriorityQueue<>(
            Comparator.comparingInt((MyInt mi) -> mi.value).reversed()
        );

        pq.offer(new MyInt(10));
        pq.offer(new MyInt(5));
        pq.offer(new MyInt(10));
        pq.offer(new MyInt(20));
        pq.offer(new MyInt(5));

        String result = "";
        while (!pq.isEmpty()) {
            result += pq.poll().value + " ";
        }
        System.out.println(result.trim());
    }
}

Q560 hard code output

What is the output of the following Java program?

java

public class MultiArrayQ6 {
    public static void main(String[] args) {
        Object[][] objMatrix = new Object[2][2];
        String[] sArray = {"Hello", "World"};
        objMatrix[0] = sArray;
        try {
            objMatrix[0][0] = 123; // Incompatible type for underlying array
        } catch (ArrayStoreException e) {
            System.out.println("ArrayStoreException caught.");
        }
        System.out.println(objMatrix[0][1]);
    }
}

☕ Java MCQ Questions – Page 28