Java MCQ Questions – Page 195 of 200

Q: Which of the following statements about method overloading is true?

C) Overloading is a form of compile-time (static) polymorphism.. Method overloading is resolved at compile time based on the method signature, making it a form of static (compile-time) polymorphism. Overloaded methods can exist in the same class, and return types can differ.

Q: What does this code print?

A) report.doc | /users/documents | image.png | null. `getName()` returns the last component of the path. `getParent()` returns the path of the parent directory, which is `null` for a file specified with only a name in the current directory.

Q: What is the primary purpose of synchronization in Java?

A) To ensure only one thread can access a shared resource at a time.. Synchronization is used to control access to shared resources, preventing data corruption and race conditions by ensuring mutual exclusion among threads.

Q: How does increasing the buffer size of a `BufferedWriter` generally impact performance for writing very large amounts of data?

B) It can improve performance by further reducing disk I/O calls, but uses more memory.. A larger buffer allows `BufferedWriter` to hold more data in memory before flushing it to the underlying `Writer`, potentially reducing the total number of expensive physical I/O operations for large data sets. However, it also consumes more memory.

Q: What will be printed when the `main` method is executed?

A) Child method. An overridden method can declare to throw a narrower (subtype) checked exception than the superclass method, or no checked exceptions. Since no exception is actually thrown at runtime, only the `Child`'s method body prints.

Q: In a performance-critical application, certain custom exceptions are thrown very frequently but are rarely logged or their stack traces inspected. Generating a full stack trace for each instance could introduce significant overhead. Which `Throwable` method can be strategically overridden in a custom exception to mitigate this performance impact?

C) `fillInStackTrace()` to return `this` without calling `super.fillInStackTrace()`, or by calling it conditionally.. The `fillInStackTrace()` method is responsible for populating the stack trace. Overriding it to return `this` (or `null` for pre-Java 1.4 compatibility) without calling `super.fillInStackTrace()` prevents the expensive stack trace generation, significantly improving performance for frequently thrown exceptions where stack trace isn't immediately needed.

Q: What is the output of this Java code?

A) true true false A B null. The ArrayBlockingQueue has a capacity of 2. `offer("C", ...)` returns `false` because the queue is full, as the timeout expires. `poll()` on an empty queue returns `null`.

Q: What is the eventual outcome of running this Java code?

C) java.lang.OutOfMemoryError: Java heap space. The 'do-while (true)' loop creates an infinite loop that continuously adds new objects to an ArrayList. This eventually exhausts the available heap memory, leading to a 'java.lang.OutOfMemoryError'.

Q: What error occurs when executing the following Java code?

B) java.lang.UnsupportedOperationException. `Arrays.asList()` returns a fixed-size `ArrayList` (a private static class within `Arrays`, not `java.util.ArrayList`) backed by the original array. Attempts to add or remove elements to this list will result in an `UnsupportedOperationException`.

Q: Identify the compile-time error in the provided Java code snippet.

A) Compile-time error: 'continue' outside of loop. The `continue` statement is used to skip the rest of the current iteration of a loop and proceed to the next iteration. It is illegal to use `continue` outside of a loop (for, while, do-while), leading to a compile-time error.

Q3881 medium

Which of the following statements about method overloading is true?

Q3882 medium code output

What does this code print?

java

import java.io.File;

public class PathComponents {
    public static void main(String[] args) {
        File file1 = new File("/users/documents/report.doc");
        File file2 = new File("image.png");
        System.out.println(file1.getName() + " | " + file1.getParent() + " | " + file2.getName() + " | " + file2.getParent());
    }
}

Q3883 easy

What is the primary purpose of synchronization in Java?

Q3884 medium

How does increasing the buffer size of a `BufferedWriter` generally impact performance for writing very large amounts of data?

Q3885 hard code output

What will be printed when the `main` method is executed?

java

class CustomException extends Exception {}
class Parent {
    void method() throws Exception { System.out.println("Parent method"); }
}
class Child extends Parent {
    @Override
    void method() throws CustomException { System.out.println("Child method"); }
}
public class Main {
    public static void main(String[] args) {
        Parent p = new Child();
        try {
            p.method();
        } catch (Exception e) {
            System.out.println("Caught: " + e.getClass().getSimpleName());
        }
    }
}

Q3886 hard

In a performance-critical application, certain custom exceptions are thrown very frequently but are rarely logged or their stack traces inspected. Generating a full stack trace for each instance could introduce significant overhead. Which `Throwable` method can be strategically overridden in a custom exception to mitigate this performance impact?

Q3887 hard code output

What is the output of this Java code?

java

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.Queue;

public class QueueTest {
    public static void main(String[] args) throws InterruptedException {
        Queue<String> queue = new ArrayBlockingQueue<>(2);

        System.out.println(queue.offer("A"));
        System.out.println(queue.offer("B"));
        System.out.println(queue.offer("C", 10, TimeUnit.MILLISECONDS));

        System.out.println(queue.poll());
        System.out.println(queue.poll(10, TimeUnit.MILLISECONDS));
        System.out.println(queue.poll(10, TimeUnit.MILLISECONDS));
    }
}

Q3888 medium code error

What is the eventual outcome of running this Java code?

java

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

public class LoopTest {
    public static void main(String[] args) {
        List<Object> storage = new ArrayList<>();
        do {
            storage.add(new Object());
        } while (true);
    }
}

Q3889 hard code error

What error occurs when executing the following Java code?

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> fixedSizeList = Arrays.asList("Red", "Green", "Blue");
        fixedSizeList.add("Yellow");
        System.out.println(fixedSizeList);
    }
}

Q3890 medium code error

Identify the compile-time error in the provided Java code snippet.

java

public class Test {
    public static void main(String[] args) {
        int value = 10;
        if (value > 5) {
            System.out.println("Condition met");
            continue;
        }
        System.out.println("End of program");
    }
}

Q3891 easy code error

What is the compile-time error in the following Java code?

java

class MyClass {
    private String data = "Hello";
}

public class Demo {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        System.out.println(obj.data);
    }
}

Q3892 hard code output

Consider the following Java code. What is the output of this code?

java

public class DirectRunCall {
    public static void main(String[] args) throws InterruptedException {
        Runnable myRunnable = () -> {
            System.out.println("Runnable running on thread: " + Thread.currentThread().getName());
        };

        System.out.println("Main thread starting...");
        myRunnable.run(); // Direct call
        new Thread(myRunnable).start(); // New thread call
        System.out.println("Main thread finished.");
    }
}

Q3893 medium

When using the `concat()` method on a String, what happens if you attempt to concatenate a `null` String reference?

Q3894 medium code error

What is the compile-time or runtime error in the following Java code snippet?

java

import java.io.*;

class Message implements Serializable {
    String content;
    public Message(String c) { this.content = c; }
}

public class SerializationQuestion9 {
    public static void main(String[] args) throws IOException {
        Message msg = new Message("Test message");
        FileOutputStream fos = new FileOutputStream("message.ser");
        ObjectOutputStream oos = new ObjectOutputStream(fos);

        fos.close(); // Closing underlying stream prematurely

        oos.writeObject(msg); // Attempting to write after stream closed
        oos.close();
    }
}

Q3895 medium code error

Consider the following Java code. What will happen when you try to compile it?

java

import java.util.Arrays;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3);
        outerLoop: for (int i = 0; i < 5; i++) {
            numbers.forEach(num -> {
                if (num == 2) {
                    break outerLoop;
                }
            });
        }
    }
}

Q3896 easy code error

What error will occur when compiling the following Java code?

java

public class Main {
    public static void main(String[] args) {
        int val = 10;
        if (!val) {
            System.out.println("Value is zero.");
        } else {
            System.out.println("Value is not zero.");
        }
    }
}

Q3897 hard code error

What is the compilation error in the following Java code?

java

interface MyConfig {
    private int TIMEOUT = 5000; // Attempt to declare a private field in an interface
    public String getSetting();
}

public class DefaultConfig implements MyConfig {
    @Override
    public String getSetting() {
        // return "Timeout: " + TIMEOUT; // This line would also fail if TIMEOUT was public
        return "Default";
    }
}

Q3898 medium code output

What does this Java code print?

java

class Dog {
    String name;
    Dog(String name) {
        this.name = name;
        System.out.println("Dog created: " + name);
    }
}
public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog("Buddy");
    }
}

Q3899 hard code error

What error will this code produce at runtime?

java

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

public class AutounboxingNPE {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(null);
        numbers.add(3);

        int total = 0;
        for (Integer num : numbers) {
            total += num;
        }
        System.out.println(total);
    }
}

Q3900 medium code error

What error occurs when compiling this code?

java

import java.io.IOException;

public class MyClass {
    public static void main(String[] args) {
        java.io.FileReader reader = new java.io.FileReader("nonexistent.txt");
        System.out.println("FileReader created.");
    }
}

☕ Java MCQ Questions – Page 195