Java MCQ Questions – Page 166 of 200

Q: Which statement regarding constructor invocation during object creation and inheritance is TRUE?

B) If a constructor explicitly calls `this()`, it cannot also explicitly call `super()`.. A constructor can only explicitly call `this()` OR `super()`, not both. An explicit `this()` call means `super()` will be implicitly called from the chained constructor, ensuring the superclass constructor is eventually invoked.

Q: What is the runtime error encountered when executing this Java code snippet?

B) java.lang.UnsupportedOperationException. `Set.of()` (introduced in Java 9) creates an unmodifiable `Set`. Any attempt to modify this set by adding or removing elements will result in an `UnsupportedOperationException`.

Q: What is the output of this code?

D) Either 'Main thread finished.\nRunnable task executed.' OR 'Runnable task executed.\nMain thread finished.', as order is not guaranteed.. When `t.start()` is called, a new thread begins execution, concurrent with the main thread. The exact order in which `System.out.println` calls from different threads execute is not guaranteed by the JVM.

Q: A thread is currently executing within a `synchronized` method. Another thread attempts to call a different `synchronized` method on the *same* object. What state does the second thread transition to?

C) BLOCKED. The second thread attempts to acquire the intrinsic lock (monitor) of the object, which is currently held by the first thread. It enters the `BLOCKED` state until the monitor becomes available.

Q: What error will occur when compiling the following Java code?

A) Compile-time error: unreported exception java.lang.InterruptedException; must be caught or declared to be thrown. `Thread.sleep()` declares that it throws an `InterruptedException`, which is a checked exception. Therefore, it must either be caught using a `try-catch` block or declared in the method signature using `throws InterruptedException`.

Q: What is the output of this code?

A) true. `equalsIgnoreCase()` performs a case-insensitive comparison according to the Unicode standard. The German 'ß' (U+00DF) uppercases to 'SS', so "Straße" becomes "STRASSE" for comparison purposes, making it equal to `s2`.

Q: What is the output of this code?

A) Programming. The `write(String str, int off, int len)` method writes `len` characters from the string `str` starting at offset `off`. Here, it writes 11 characters starting from index 0, which is "Programming".

Q: What is the output of this code?

C) java.lang.ClassCastException. The element at index 0 is an `Integer` object (`100`). Attempting to cast an `Integer` directly to a `String` at runtime will result in a `ClassCastException`.

Q: What is the primary purpose of the `finally` block in Java exception handling?

B) To execute cleanup code regardless of whether an exception occurred or not.. The `finally` block guarantees that its code will be executed, typically for cleanup operations like closing resources, whether an exception was thrown and caught or not.

Q: What is the error in the following Java code?

B) The code will not compile because `TreeSet` does not have a `get(int index)` method.. `TreeSet` implements the `Set` interface, which does not define a `get(int index)` method because sets do not maintain elements by index. This method is typically found in `List` implementations. Attempting to call `get(0)` on a `TreeSet` will result in a compile-time error.

Q3301 hard

Which statement regarding constructor invocation during object creation and inheritance is TRUE?

Q3302 hard code error

What is the runtime error encountered when executing this Java code snippet?

java

import java.util.Set;
import java.util.HashSet;

public class Main {
    public static void main(String[] args) {
        Set<String> immutableSet = Set.of("apple", "banana"); // Java 9+ immutable set
        immutableSet.remove("apple"); // Attempt to modify immutable set
    }
}

Q3303 medium code output

What is the output of this code?

java

class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Runnable task executed.");
    }
}

public class Main {
    public static void main(String[] args) {
        MyRunnable r = new MyRunnable();
        Thread t = new Thread(r);
        t.start();
        System.out.println("Main thread finished.");
    }
}

Q3304 hard

A thread is currently executing within a `synchronized` method. Another thread attempts to call a different `synchronized` method on the *same* object. What state does the second thread transition to?

Q3305 medium code error

What error will occur when compiling the following Java code?

java

public class SleepUnhandledException {
    public void methodWithSleep() {
        Thread.sleep(100); // InterruptedException is a checked exception
    }
    public static void main(String[] args) {
        new SleepUnhandledException().methodWithSleep();
    }
}

Q3306 hard code output

What is the output of this code?

java

public class StringEqualsIgnoreCaseTest {
    public static void main(String[] args) {
        String s1 = "Straße"; // German sharp s (ß)
        String s2 = "STRASSE";
        System.out.println(s1.equalsIgnoreCase(s2));
    }
}

Q3307 easy code output

What is the output of this code?

java

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

public class Main {
    public static void main(String[] args) {
        StringWriter stringWriter = new StringWriter();
        try (BufferedWriter writer = new BufferedWriter(stringWriter)) {
            String data = "Programming Language";
            writer.write(data, 0, 11);
            writer.flush();
            System.out.print(stringWriter.toString());
        } catch (IOException e) {
            System.out.print("Error");
        }
    }
}

Q3308 hard code error

What is the output of this code?

java

import java.util.LinkedList;
import java.util.Arrays;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<Object> mixedList = new LinkedList<>(Arrays.asList(100, "Hello", true));
        String s = (String) mixedList.get(0); // Attempt to cast Integer to String
        System.out.println(s);
    }
}

Q3309 easy

What is the primary purpose of the `finally` block in Java exception handling?

Q3310 easy code error

What is the error in the following Java code?

java

import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        TreeSet<Integer> numbers = new TreeSet<>();
        numbers.add(10);
        numbers.add(20);
        int first = numbers.get(0);
    }
}

Q3311 medium

Which Java String method would return `true` for a string containing only space characters (e.g., `" "`), but `false` for an empty string (e.g., `""`)?

Q3312 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, String> dictionary = new HashMap<>();
        System.out.println(dictionary.isEmpty());
        dictionary.put("Hello", "Greeting");
        System.out.println(dictionary.isEmpty());
    }
}

Q3313 medium code error

What error will this Java code produce when executed?

java

public class ArrayError {
    public static void main(String[] args) {
        int[][] matrix = new int[3][];
        System.out.println(matrix[0][0]);
    }
}

Q3314 hard

Which of the following is the primary functional difference between `String.trim()` and `String.strip()`?

Q3315 hard

If a `switch` expression (Java 14+) has different branches that `yield` values of distinct but compatible types (e.g., one `yield`s an `Integer` and another `yield`s a `Double`), what will be the resulting compile-time type of the `switch` expression?

Q3316 hard

`FileWriter` constructors do not directly accept a `Charset` object to specify the encoding. If a specific encoding (e.g., UTF-16) is required for a file, how would you best achieve this using the `FileWriter`'s underlying mechanisms?

Q3317 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> nums = new ArrayList<>();
        nums.add(1);
        nums.add(4);
        nums.add(2);
        nums.add(5);
        Iterator<Integer> it = nums.iterator();
        while (it.hasNext()) {
            Integer num = it.next();
            if (num > 2) {
                System.out.print(num);
            }
        }
    }
}

Q3318 hard code output

Assume a file named 'test.txt' exists with the content "Hello". What is the output of this code?

java

import java.io.FileReader;
import java.io.IOException;
import java.io.File;

public class FileReaderMark {
    public static void main(String[] args) throws IOException {
        // Assume 'test.txt' exists and contains "Hello"
        try (FileReader reader = new FileReader(new File("test.txt"))) {
            System.out.println("Mark Supported: " + reader.markSupported());
            reader.mark(10); // Attempt to mark
            reader.read(); // Read 'H'
            reader.reset(); // Attempt to reset
            int c = reader.read(); 
            System.out.println("After reset, read: " + (char) c);
        }
    }
}

Q3319 easy code output

What is the output of this Java program?

java

public class MyClass {
    public static void main(String[] args) {
        int x = 1;
        switch (x) {
            case 1: System.out.print("One");
            case 2: System.out.print("Two");
            case 3: System.out.print("Three"); break;
            default: System.out.print("Other");
        }
    }
}

Q3320 easy code output

What does this code print when executed?

java

public class Wallet {
    private int balance;

    public Wallet(int initialBalance) {
        this.balance = initialBalance;
    }

    public void deposit(int amount) {
        if (amount > 0) {
            balance += amount;
        }
    }

    public int getBalance() {
        return balance;
    }

    public static void main(String[] args) {
        Wallet myWallet = new Wallet(100);
        myWallet.deposit(50);
        myWallet.deposit(-20);
        System.out.println(myWallet.getBalance());
    }
}

☕ Java MCQ Questions – Page 166