Java MCQ Questions – Page 178 of 200

Q: A `DelayQueue` is designed to hold elements that implement the `Delayed` interface. What is the primary characteristic governing when elements can be removed from a `DelayQueue`?

B) Elements can only be removed after their associated delay has expired, with the element having the smallest remaining delay being removed first.. DelayQueue elements can only be removed when their delay has expired. The `poll()` and `take()` methods only retrieve elements whose `getDelay()` method returns zero or less, effectively making it a time-based priority queue.

Q: What is the output of this Java code?

A) Hello: World. The lambda expression implements the `print` method, prepending 'Hello: ' to the input message. When 'World' is passed, it prints 'Hello: World'.

Q: What is the output of this Java code?

A) Caught NullPointerException. The code attempts to get the length of a null string, which throws a `NullPointerException`. The JVM then looks for the most specific `catch` block that can handle this exception. The `catch (NullPointerException e)` block is the first matching block and is executed.

Q: What is the error in this Java code snippet?

A) A compile-time error: Incompatible types: StringBuilder cannot be converted to String.. A StringBuilder object cannot be directly assigned to a String reference because they are different types and 'StringBuilder' does not implicitly convert to 'String'. The 'toString()' method must be explicitly called for conversion.

Q: Which statement is most accurate regarding `Thread.setPriority()` in Java?

C) Thread priorities are hints to the scheduler, and their effect can vary significantly across different operating systems and JVM implementations; they do not guarantee execution order.. Java thread priorities are merely hints to the underlying operating system's scheduler. Their actual effect is platform-dependent and not guaranteed, and they do not prevent lower-priority threads from eventually running (unless the scheduler is specifically configured to do so).

Q: What is the error encountered when running this Java code?

C) IndexOutOfBoundsException. The 'read(char[] cbuf, int off, int len)' method throws an IndexOutOfBoundsException if 'off' is negative, 'len' is negative, or 'off + len' is greater than 'cbuf.length'. In this case, 5 + 10 = 15, which exceeds the buffer's length of 10.

Q: A `protected` member of a superclass is accessible in a subclass:

C) Regardless of whether the subclass is in the same package or a different package.. `protected` members are accessible within the same package and by all subclasses, regardless of their package.

Q: What is the output of this code?

A) 30. The `put` method adds a key-value pair to the HashMap. The `get` method retrieves the value associated with the specified key. In this case, 'Alice' is associated with the value 30.

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

A) `continue outside of loop`. A `continue` statement can only be used directly within a loop. An anonymous class's method body is not considered a loop, even if the method is invoked from within a loop.

Q: Which line causes a compilation error regarding method visibility?

B) Line 8: `private void methodA() {`. An overridden method cannot reduce the visibility of the superclass method. Attempting to override a `public` method with a `private` method results in a compile-time error on Line 8.

Q3541 hard

A `DelayQueue` is designed to hold elements that implement the `Delayed` interface. What is the primary characteristic governing when elements can be removed from a `DelayQueue`?

Q3542 easy code output

What is the output of this Java code?

java

interface SimplePrinter {
    void print(String message);
}

public class Main {
    public static void main(String[] args) {
        SimplePrinter printer = (msg) -> System.out.println("Hello: " + msg);
        printer.print("World");
    }
}

Q3543 medium code output

What is the output of this Java code?

java

public class MultipleCatchBlocks {
    public static void main(String[] args) {
        try {
            String s = null;
            System.out.println(s.length()); // NullPointerException
        } catch (ArithmeticException e) {
            System.out.println("Caught ArithmeticException");
        } catch (NullPointerException e) {
            System.out.println("Caught NullPointerException");
        } catch (Exception e) {
            System.out.println("Caught general Exception");
        }
    }
}

Q3544 medium code error

What is the error in this Java code snippet?

java

public class MyClass {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Test");
        String s = sb;
        System.out.println(s);
    }
}

Q3545 hard

Which statement is most accurate regarding `Thread.setPriority()` in Java?

Q3546 hard code error

What is the error encountered when running this Java code?

java

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

public class FileReaderError3 {
    public static void main(String[] args) {
        File file = new File("test_fr3.txt");
        try {
            file.createNewFile();
            try (FileReader fr = new FileReader(file)) {
                char[] buffer = new char[10];
                fr.read(buffer, 5, 10); // buffer size 10, offset 5, length 10. 5+10 = 15 > 10
                System.out.println("Read successfully");
            }
        } catch (IOException e) {
            System.err.println(e.getClass().getSimpleName() + ": " + e.getMessage());
        } catch (IndexOutOfBoundsException e) {
            System.err.println(e.getClass().getSimpleName());
        } finally {
            file.delete();
        }
    }
}

Q3547 medium

A `protected` member of a superclass is accessible in a subclass:

Q3548 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> ages = new HashMap<>();
        ages.put("Alice", 30);
        ages.put("Bob", 25);
        System.out.println(ages.get("Alice"));
    }
}

Q3549 hard code error

What compilation error will occur when compiling this Java code?

java

public class AnonClassContinue {
    interface Task {
        void execute(int val);
    }
    public static void main(String[] args) {
        for (int i = 0; i < 3; i++) {
            Task task = new Task() {
                @Override
                public void execute(int val) {
                    if (val == 1) {
                        continue;
                    }
                    System.out.println("Executing for: " + val);
                }
            };
            task.execute(i);
        }
    }
}

Q3550 hard code error

Which line causes a compilation error regarding method visibility?

java

class AccessParent {
    public void methodA() {
        System.out.println("Parent methodA");
    }
}
class AccessChild extends AccessParent {
    @Override
    private void methodA() { // Line 8
        System.out.println("Child methodA");
    }
}
public class Permissions {
    public static void main(String[] args) {
        AccessParent ap = new AccessChild();
        ap.methodA();
    }
}

Q3551 easy

When defining a custom exception, what is a common practice for its constructors?

Q3552 easy code error

What will happen when you try to compile this Java code?

java

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < 3; i++) {
            if (i == 1) {
                continue innerLoop;
            }
            System.out.println(i);
        }
    }
}

Q3553 hard code error

What is the compilation error in the following Java code snippet?

java

import java.io.IOException;
import java.util.function.Consumer;

public class Main {
    public static void main(String[] args) {
        Consumer<String> fileWriter = s -> {
            // This lambda attempts to throw a checked exception
            throw new IOException("Failed to write: " + s);
        };
        System.out.println("Attempting to assign lambda...");
    }
}

Q3554 easy code error

What error will occur during deserialization if `data.ser` was created with `MyData` having `serialVersionUID = 1L`, but the current `MyData` class has `serialVersionUID = 2L`?

java

import java.io.*;

class MyData implements Serializable {
    private static final long serialVersionUID = 2L; // Current version ID
    String value;
    public MyData(String value) { this.value = value; }
}

public class Main {
    public static void main(String[] args) {
        // Assume "data.ser" was created by serializing a MyData object
        // where MyData had serialVersionUID = 1L
        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("data.ser"))) {
            MyData data = (MyData) ois.readObject(); // Mismatch occurs here
            System.out.println(data.value);
        } catch (IOException | ClassNotFoundException e) {
            System.err.println(e.getClass().getSimpleName() + ": " + e.getMessage());
        }
    }
}

Q3555 hard code error

What error occurs when attempting to compile the following Java code?

java

public class OrphanElseIf {
    public static void main(String[] args) {
        int score = 85;
        if (score > 90) {
            System.out.println("Grade A");
        }
        // This 'else if' is orphaned as the preceding 'if' block is closed.
        else if (score > 80) { // 'else' without 'if'
            System.out.println("Grade B");
        } else {
            System.out.println("Grade C");
        }
    }
}

Q3556 easy code error

What error will be encountered when compiling the following Java snippet?

java

class OuterClass {
    private class InnerClass {
        String message = "Inner";
    }
}

public class Application {
    public static void main(String[] args) {
        OuterClass outer = new OuterClass();
        OuterClass.InnerClass inner = outer.new InnerClass();
        System.out.println(inner.message);
    }
}

Q3557 hard

When designing a producer-consumer system with a bounded buffer, why is it generally recommended to use `offer()` and `poll()` methods of a `BlockingQueue` rather than `add()` and `remove()`?

Q3558 easy code output

What is the output of this code?

java

class Parent {
    String message = "Hello from Parent";
}

class Child extends Parent {
    String message = "Hello from Child";
    void printMessage() {
        System.out.println(message);
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        c.printMessage();
    }
}

Q3559 medium

Consider a `TreeMap<Integer, String> map`. If `map.headMap(5)` is called, which keys will be included in the returned sub-map?

Q3560 easy code output

What does this code print?

java

public class CurrentThreadInfo {
    public static void main(String[] args) {
        System.out.println("Current thread: " + Thread.currentThread().getName());
    }
}

☕ Java MCQ Questions – Page 178