Java MCQ Questions – Page 36 of 200

Q: What is the typical growth factor for an `ArrayList`'s internal array when it needs to expand its capacity in Java?

B) It increases by 50% (current capacity + current capacity / 2).. When an `ArrayList` needs to grow, its capacity is typically increased by 50% of its current capacity (newCapacity = oldCapacity + oldCapacity >> 1).

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

A) incompatible types: HashSet cannot be converted to Set . You cannot assign a `HashSet ` to a `Set ` reference because their generic types are incompatible. This is a compile-time type mismatch error.

Q: What error will this Java code produce when compiled and run?

A) java.lang.NegativeArraySizeException. The expression `x - y` (10 - 20) results in -10. Casting -10 to a `byte` still results in -10. When a negative value is passed to an array constructor (e.g., `new int[-10]`), Java throws a `NegativeArraySizeException` at runtime.

Q: What is the expected error when compiling and running the following Java code?

A) Compile-time error: cannot find symbol 'removeFirst()'. While `list` is an instance of `LinkedList` at runtime, its compile-time type is `List`. The `List` interface does not declare `removeFirst()`, which is a specific method of the `LinkedList` class, leading to a compile-time error.

Q: Which type of variable can be accessed directly from both instance methods and static methods, but requires an object reference when accessed from a static context?

C) Instance variable. Instance variables belong to objects. Instance methods can access them directly because they operate on an object. Static methods, which do not operate on a specific object, require an explicit object reference to access an instance variable.

Q: What kind of error will occur when executing this Java code?

B) NullPointerException. A TreeSet (without a custom Comparator handling nulls) does not allow null elements once other non-null elements have been added. When add(null) is called after 10 and 20, it attempts to compare null with an existing element using natural ordering, resulting in a NullPointerException.

Q: What happens when a thread calls `Thread.sleep(long millis)`?

B) The current thread pauses execution for at least the specified duration, without releasing any monitor locks it holds, and enters the TIMED_WAITING state.. `Thread.sleep()` causes the currently executing thread to cease execution for the specified number of milliseconds. It does not release any locks that the thread may be holding.

Q: What does this code print?

B) Hello World. The `+` operator concatenates strings. It joins "Hello", a space, and "World" into a single string "Hello World".

Q: What does this code print?

A) true true false. `ready()` initially returns `true` as data is available. After reading 'First', 'Second' is still available (either in the buffer or underlying stream), so it's `true`. After reading 'Second', the stream is at its end, thus `false`.

Q: What is the output of this code?

A) Compile-time error: MyTask is not abstract and does not override abstract method run() in Runnable. The `run()` method in the `Runnable` interface is `public`. Omitting the `public` modifier in the implementing class reduces its visibility, thus not satisfying the interface contract and leading to a compile-time error.

Q701 medium

What is the typical growth factor for an `ArrayList`'s internal array when it needs to expand its capacity in Java?

Q702 easy code error

What error will occur when compiling the following Java code?

java

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

public class MyClass {
    public static void main(String[] args) {
        Set<String> s = new HashSet<Integer>(); // This line will cause an error
        s.add("test");
        System.out.println(s.size());
    }
}

Q703 hard code error

What error will this Java code produce when compiled and run?

java

public class NegativeSizeArray {
    public static void main(String[] args) {
        int x = 10;
        byte y = 20;
        // Calculation results in a negative value for array size
        int size = (byte)(x - y); 
        int[] arr = new int[size];
        System.out.println("Array created successfully.");
    }
}

Q704 easy code error

What is the expected error when compiling and running the following Java code?

java

import java.util.List;
import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        List<String> list = new LinkedList<>();
        list.add("Item");
        list.removeFirst(); // Method specific to LinkedList, not List interface
    }
}

Q705 medium

Which type of variable can be accessed directly from both instance methods and static methods, but requires an object reference when accessed from a static context?

Q706 medium code error

What kind of error will occur when executing this Java code?

java

import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        TreeSet<Integer> set = new TreeSet<>();
        set.add(10);
        set.add(20);
        set.add(null);
        System.out.println(set);
    }
}

Q707 medium

What happens when a thread calls `Thread.sleep(long millis)`?

Q708 easy code output

What does this code print?

java

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

Q709 medium code output

What does this code print?

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\nSecond";
        try (BufferedReader br = new BufferedReader(new StringReader(data))) {
            System.out.println(br.ready());
            br.readLine();
            System.out.println(br.ready());
            br.readLine();
            System.out.println(br.ready());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q710 hard code error

What is the output of this code?

java

class MyTask implements Runnable {
    // This is not a valid override for Runnable.run() because of reduced visibility
    void run() { 
        System.out.println("Task running.");
    }
}

public class Main {
    public static void main(String[] args) {
        MyTask task = new MyTask();
        Thread t = new Thread(task);
        t.start();
    }
}

Q711 hard

Given the following Java class: java class Overload { void method(long l) { System.out.println("long"); } void method(Integer i) { System.out.println("Integer"); } } What will be printed when the following code is executed? `new Overload().method(5);`

Q712 hard code error

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

java

public class StringCompareToNull {
    public static void main(String[] args) {
        String s1 = "alpha";
        String s2 = null;
        try {
            int result = s1.compareTo(s2);
            System.out.println(result);
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

Q713 hard code output

What is the output of this Java code snippet?

java

interface A { default void foo() { System.out.println("Interface A"); } }
interface B { default void foo() { System.out.println("Interface B"); } }
class C implements A, B {
    @Override public void foo() { System.out.println("Class C"); }
}
class D implements A, B {
    @Override public void foo() { A.super.foo(); }
}
public class Main {
    public static void main(String[] args) {
        new C().foo();
        new D().foo();
    }
}

Q714 easy

Which of the following is NOT a primitive type that can be directly type-cast in Java?

Q715 easy code output

What is the output of the following Java program?

java

public class LoopTest {
    public static void main(String[] args) {
        int i = 1;
        do {
            System.out.println("Iteration: " + i);
            i++;
        } while (i < 3);
    }
}

Q716 medium code error

What is the result of attempting to run the following Java code?

java

public class Main {
    public static void main(String[] args) {
        Thread daemonThread = new Thread(() -> {
            try {
                System.out.println("Daemon thread running...");
                Thread.sleep(100);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        });
        daemonThread.start();
        daemonThread.setDaemon(true); // This line
        System.out.println("Main thread exiting.");
    }
}

Q717 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> inventory = new HashMap<>();
        inventory.put("Apple", 10);
        inventory.put("Banana", 5);
        inventory.clear();
        System.out.println(inventory.size());
    }
}

Q718 hard code output

What is the output of this Java code?

java

import java.io.FileWriter;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
import java.nio.file.Files;
import java.nio.file.Path;

public class FileWriterTruncation {
    public static void main(String[] args) {
        String filename = "test_truncation.txt";
        try {
            try (FileWriter fw = new FileWriter(filename)) { fw.write("Line A\nLine B\n"); }
            try (FileWriter fw = new FileWriter(filename)) { fw.write("Line C"); }

            try (BufferedReader br = new BufferedReader(new FileReader(filename))) {
                String line; while ((line = br.readLine()) != null) { System.out.println(line); }
            }
        } catch (IOException e) { System.out.println("Error: " + e.getMessage());
        } finally { try { Files.deleteIfExists(Path.of(filename)); } catch (IOException ignored) {} }
    }
}

Q719 easy

What exception is thrown if you call `next()` on an `Iterator` when there are no more elements?

Q720 medium code output

What is the output of this Java code?

java

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

public class Main {
    public static void main(String[] args) {
        Set<String> items = new HashSet<>();
        items.add("ItemA");
        items.add("ItemB");
        items.clear();
        System.out.println(items.isEmpty());
    }
}

☕ Java MCQ Questions – Page 36