Java MCQ Questions – Page 172 of 200

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

A) java.lang.NullPointerException. The `String` constructor `new String(byte[] bytes, String charsetName)` expects a non-null `charsetName`. Passing `null` will cause a `NullPointerException` at runtime.

Q: What does this code print?

A) Limit exceeded! LimitExceededException. The `checkLimit` method throws `LimitExceededException` because 150 > 100. This is caught, and the `catch` block prints 'Limit exceeded!' followed by the simple name of the exception class, which is `LimitExceededException`.

Q: In which major version of Java were Lambda Expressions officially introduced?

C) Java 8. Lambda Expressions, along with the Stream API, were major features introduced in Java 8, released in 2014.

Q: What error will be thrown by the `MyTask` thread when the `main` thread interrupts it?

B) No error will be thrown, the message "Task interrupted" will be printed to stderr.. When `Thread.sleep()` is interrupted, it throws an `InterruptedException`. In this code, the exception is caught and its message is printed, but it is not re-thrown or handled in a way that would stop the program. Therefore, no error propagates to the `main` method.

Q: What kind of error will occur when compiling or running the following Java code?

A) java.lang.StringIndexOutOfBoundsException. The `setCharAt(int index, char ch)` method requires the index to be between `0` and `length() - 1`. Attempting to set a character at `sb.length()` (index 4 for a length-4 string) is out of bounds, resulting in a `StringIndexOutOfBoundsException`.

Q: What error occurs when compiling this Java code?

A) Compilation error: Unhandled exception type java.net.URISyntaxException. A constructor, like any other method, must either catch a checked exception it throws (`URISyntaxException` is checked) or declare it using a `throws` clause. Since neither is done, a compilation error occurs.

Q: What will be the result of compiling this Java code?

A) Compile-time error: Implicit super constructor Base() is not visible.. Every constructor implicitly or explicitly calls a superclass constructor. Since `Base`'s only constructor is private, it's not accessible to `Derived`, resulting in a compile-time error. `Derived` cannot call `super()` even implicitly.

Q: What does this code print?

A) Direct run call.. This code does not involve threads. It simply defines a class with a `run()` method and then calls that method directly from `main`, just like any other method call. It will print the message.

Q: Can constructors in Java be overloaded?

C) Yes, by having different parameter lists.. Constructors can indeed be overloaded in Java, allowing a class to have multiple constructors with different parameter lists to initialize objects in various ways.

Q: When a thread attempts to enter a `synchronized` block or method but the monitor is currently held by another thread, what state does the attempting thread enter?

D) BLOCKED. If a thread cannot acquire the monitor lock required to enter a synchronized block or method, it enters the BLOCKED state. It waits here until the lock becomes available.

Q3421 hard code error

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

java

import java.nio.charset.Charset;

public class CharsetNullConstructor {
    public static void main(String[] args) {
        byte[] bytes = {72, 101, 108, 108, 111}; // ASCII for "Hello"
        String charsetName = null;
        try {
            String s = new String(bytes, charsetName);
            System.out.println(s);
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q3422 easy code output

What does this code print?

java

class LimitExceededException extends RuntimeException {
    public LimitExceededException() {
        // Default constructor, relies on parent's default
    }
}

public class Main {
    public static void checkLimit(int value) {
        if (value > 100) {
            throw new LimitExceededException();
        }
    }

    public static void main(String[] args) {
        try {
            checkLimit(150);
        } catch (LimitExceededException e) {
            System.out.println("Limit exceeded!");
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q3423 easy

In which major version of Java were Lambda Expressions officially introduced?

Q3424 hard code error

What error will be thrown by the `MyTask` thread when the `main` thread interrupts it?

java

class MyTask implements Runnable {
    @Override
    public void run() {
        try {
            System.out.println("Task sleeping...");
            Thread.sleep(5000);
            System.out.println("Task woke up normally.");
        } catch (InterruptedException e) {
            // Exception caught but not handled correctly, it's just printed
            System.err.println("Task interrupted: " + e.getMessage());
        }
    }
}

public class InterruptExample {
    public static void main(String[] args) throws InterruptedException {
        Thread t = new Thread(new MyTask());
        t.start();
        Thread.sleep(100); 
        t.interrupt(); // Interrupt the sleeping thread
    }
}

Q3425 hard code error

What kind of error will occur when compiling or running the following Java code?

java

public class SBError {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Data"); // Length 4
        sb.setCharAt(sb.length(), '!'); // Attempt to set char at index 4
        System.out.println(sb);
    }
}

Q3426 medium code error

What error occurs when compiling this Java code?

java

import java.net.URISyntaxException;

public class MyResource {
    public MyResource() {
        // Simulate an operation that might throw URISyntaxException
        throw new URISyntaxException("invalid uri", "description");
    }

    public static void main(String[] args) {
        // Nothing happens here
    }
}

Q3427 hard code error

What will be the result of compiling this Java code?

java

class Base {
    private Base() {
        System.out.println("Base constructor");
    }
}
class Derived extends Base {
    public Derived() {
        // super(); // Implicit or explicit call to Base() is needed
        System.out.println("Derived constructor");
    }
    public static void main(String[] args) {
        Derived d = new Derived();
    }
}

Q3428 easy code output

What does this code print?

java

public class DirectRunCall {
    public void run() {
        System.out.println("Direct run call.");
    }

    public static void main(String[] args) {
        DirectRunCall obj = new DirectRunCall();
        obj.run();
    }
}

Q3429 easy

Can constructors in Java be overloaded?

Q3430 medium

When a thread attempts to enter a `synchronized` block or method but the monitor is currently held by another thread, what state does the attempting thread enter?

Q3431 easy

Which of the following is a common characteristic of a class designed to be immutable?

Q3432 medium code error

What error will occur when compiling this Java code?

java

public class ConditionCheck {
    public static void main(String[] args) {
        int counter = 0;
        if (counter == 0) {
            System.out.println("Starting count.");
            break;
        }
        System.out.println("Counted.");
    }
}

Q3433 medium code output

What is the output of this code?

java

class VolatileExample {
    private volatile boolean flag = false;
    private int value = 0;

    public void writer() {
        value = 123;
        flag = true;
    }

    public void reader() {
        while (!flag) {
            Thread.yield();
        }
        System.out.println("Value is: " + value);
    }
}

public class Main {
    public static void main(String[] args) throws InterruptedException {
        VolatileExample example = new VolatileExample();
        Thread writer = new Thread(example::writer);
        Thread reader = new Thread(example::reader);

        reader.start();
        Thread.sleep(100); 
        writer.start();

        writer.join();
        reader.join();
    }
}

Q3434 medium

When an object is serialized, what happens to its `static` fields?

Q3435 easy code output

What does this code print?

java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        Iterator<Integer> it = numbers.iterator();
        while (it.hasNext()) {
            System.out.print(it.next());
        }
    }
}

Q3436 easy code output

What is the output of this Java code snippet?

java

public class Test {
    public static void main(String[] args) {
        int[] data = {100};
        System.out.println(data.length - 1);
    }
}

Q3437 medium code error

What error does this Java code produce when executed?

java

public class Main {
    public static void main(String[] args) {
        String text = null;
        System.out.println(text.length());
    }
}

Q3438 easy code output

What is the output of this Java code?

java

public class MyClass {
    public static void riskyMethod() {
        System.out.println("Attempting operation...");
        throw new IllegalArgumentException("Invalid input");
    }

    public static void main(String[] args) {
        riskyMethod();
        System.out.println("Operation completed.");
    }
}

Q3439 medium code output

What does this Java code print?

java

public class Main {
    public static void main(String[] args) {
        System.out.println("Before sleep.");
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            System.out.println("Interrupted during sleep.");
        }
        System.out.println("After sleep.");
    }
}

Q3440 medium

Consider a `BufferedReader` reading from a large file. If `mark()` is called, what is a potential issue if the `readAheadLimit` specified is too small?

☕ Java MCQ Questions – Page 172