Java MCQ Questions – Page 16 of 200

Q: A developer encounters issues on Windows with `File` operations (e.g., `exists()`, `delete()`) failing for paths exceeding approximately 260 characters. What is the fundamental reason for this behavior when using `java.io.File`?

A) `java.io.File` internally relies on legacy Win32 API calls that have a hardcoded `MAX_PATH` limit, which it does not automatically bypass using extended path prefixes (`\\?\`).. The `java.io.File` class often interacts with the native OS filesystem via legacy APIs which, on Windows, typically have a `MAX_PATH` limit of 260 characters. The newer `java.nio.file.Path` API offers better support for longer paths by using extended path prefixes.

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

A) Error: unreported exception java.io.IOException; must be caught or declared to be thrown. A lambda expression cannot throw a checked exception unless the functional interface's SAM (Single Abstract Method) signature declares that exception, or the exception is caught within the lambda body. Here, `MyConsumer.accept` does not declare `IOException`, so the compiler reports it as an unreported exception.

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

B) array initializer not allowed here. An array initializer like `{"Red", "Green", "Blue"}` can only be used in a declaration or explicit array creation (`new String[]{"Red", ...}`). It cannot be used directly as a method argument for `addAll`, which expects a `Collection`.

Q: What does this code print?

A) null. `poll()` is designed to return `null` if the queue is empty, rather than throwing an exception. This makes it a safer option for retrieving elements.

Q: What is the primary purpose of using the `instanceof` operator before performing a downcast in Java?

C) To check if an object is an instance of a specific class or interface, preventing `ClassCastException`.. The `instanceof` operator is used to verify if an object is indeed an instance of a particular class or an interface, or a subclass thereof. This check helps avoid a `ClassCastException` that would occur during an invalid downcast.

Q: What is the output of this code?

A) 1: false 2: true 3: Third 4: false 5: true. First `readLine()` gets "First" (not empty). Second gets "" (empty line). Third gets "Third". Fourth gets "" (from the trailing newline). Fifth gets `null` (end of stream).

Q: What compile-time error will occur in the `main` method?

A) error: unreported exception MyCustomCheckedException; must be caught or declared to be thrown. `MyCustomCheckedException` is a checked exception. The `catch (Error e)` block cannot handle it because `Error` is not a superclass of `MyCustomCheckedException` (which extends `Exception`). Thus, the exception remains unreported.

Q: Which type of loop is a do-while loop categorized as?

A) Exit-controlled loop. A do-while loop is an exit-controlled loop because its condition is checked at the 'exit' point after the loop body has executed.

Q: What is the output of this Java code?

A) Try block Finally block Returned from try. When a 'return' statement is encountered in the 'try' block, the 'finally' block is executed immediately afterward, before the method exits and returns the specified value.

Q: What is the compile-time error in the `Beta` class?

C) The `show()` method in `Alpha` is not inherited by `Beta`, making the `@Override` annotation invalid.. `private` methods are not inherited by subclasses, and therefore cannot be overridden. The `@Override` annotation correctly flags this compile-time error on Line 8.

Q301 hard

A developer encounters issues on Windows with `File` operations (e.g., `exists()`, `delete()`) failing for paths exceeding approximately 260 characters. What is the fundamental reason for this behavior when using `java.io.File`?

Q302 hard code error

What compilation error will occur when compiling the following Java code?

java

import java.io.IOException;

interface MyConsumer<T> {
    void accept(T t);
}

public class LambdaCheckedException {
    public static void main(String[] args) {
        MyConsumer<String> mc = s -> {
            throw new IOException("Simulated IO error");
        };
    }
}

Q303 easy code error

What error will occur when compiling the following Java code?

java

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

public class MyClass {
    public static void main(String[] args) {
        Set<String> colors = new HashSet<>();
        colors.addAll({"Red", "Green", "Blue"}); // This line will cause an error
        System.out.println(colors.size());
    }
}

Q304 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<String> myQueue = new LinkedList<>();
        System.out.println(myQueue.poll());
    }
}

Q305 medium

What is the primary purpose of using the `instanceof` operator before performing a downcast in Java?

Q306 medium code output

What is the output of this code?

java

import java.io.BufferedReader;
import java.io.StringReader;
import java.io.IOException;

public class BufferedReaderTest {
    public static void main(String[] args) {
        String data = "First\n\nThird\n";
        try (BufferedReader br = new BufferedReader(new StringReader(data))) {
            System.out.println("1: " + br.readLine().isEmpty());
            System.out.println("2: " + br.readLine().isEmpty());
            System.out.println("3: " + br.readLine());
            System.out.println("4: " + (br.readLine() == null));
            System.out.println("5: " + (br.readLine() == null));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q307 easy code error

What compile-time error will occur in the `main` method?

java

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

public class Main {
    public static void someMethod() throws MyCustomCheckedException {
        throw new MyCustomCheckedException("Specific error");
    }

    public static void main(String[] args) {
        try {
            someMethod();
        } catch (Error e) { // This catch block cannot handle MyCustomCheckedException
            System.out.println("Caught an error: " + e.getMessage());
        }
    }
}

Q308 easy

Which type of loop is a do-while loop categorized as?

Q309 medium code error

What is the output of this Java code?

java

public class ExceptionFlow3 {
    public static void main(String[] args) {
        System.out.println(testMethod());
    }

    public static String testMethod() {
        try {
            System.out.println("Try block");
            return "Returned from try";
        } catch (Exception e) {
            System.out.println("Catch block");
            return "Returned from catch";
        } finally {
            System.out.println("Finally block");
        }
    }
}

Q310 hard code error

What is the compile-time error in the `Beta` class?

java

class Alpha {
    private void show() {
        System.out.println("Alpha show");
    }
}
class Beta extends Alpha {
    @Override
    public void show() { // Line 8
        System.out.println("Beta show");
    }
}
public class Driver {
    public static void main(String[] args) {
        Beta b = new Beta();
        b.show();
    }
}

Q311 hard code output

What will be printed to the console?

java

public class MultiArrayQ4 {
    public static void main(String[] args) {
        int[][] data = new int[2][];
        data[0] = new int[3];
        data[1] = null;
        try {
            System.out.println(data[1][0]);
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q312 medium code output

What is the output of this code?

java

public class StringTest {
    public static void main(String[] args) {
        String s1 = "  Hello World  ";
        String s2 = s1.trim();
        System.out.println(s2.length());
    }
}

Q313 easy code output

What does this program print?

java

public class Point {
    private int x;
    private int y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int sumCoordinates() {
        return x + y;
    }

    public static void main(String[] args) {
        Point p1 = new Point(5, 10);
        System.out.println(p1.sumCoordinates());
    }
}

Q314 easy code error

Find the compile-time error in the following Java code.

java

public class DataTypeNegativeCharError {
    public static void main(String[] args) {
        char unicodeChar = -5;
        System.out.println(unicodeChar);
    }
}

Q315 easy code error

What compile-time error will occur in the lambda expression?

java

import java.util.concurrent.Callable;

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

public class Main {
    public static void main(String[] args) {
        Callable<String> task = () -> {
            if (true) {
                // Checked exception thrown without being caught or declared
                throw new TaskFailedException("Task could not be completed"); 
            }
            return "Success";
        };
        // No direct call to task.call() here, error is in lambda definition
    }
}

Q316 easy

Can an abstract class be instantiated directly in Java?

Q317 hard

What is the precise return value of `BufferedReader.readLine()` when it reaches the end of the stream without any more characters to read, after processing all previous lines?

Q318 easy code output

What is the output of this Java code?

java

public class LoopTask implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 3; i++) {
            System.out.println("Loop iteration: " + i);
        }
    }

    public static void main(String[] args) {
        new Thread(new LoopTask()).start();
    }
}

Q319 medium code error

What is the compilation error in the provided Java code?

java

interface Service {
    void execute();
}

interface AdvancedService extends Service {
    void setup();
}

public class MyService {
    // Missing implementation
}

Q320 easy code error

What error will occur when compiling the following Java code?

java

public class Main {
    public static void main(String[] args) {
        boolean flag = true;
        int result = ~flag;
        System.out.println(result);
    }
}

☕ Java MCQ Questions – Page 16