☕ Java MCQ Questions – Page 37

public class Main {
    public static void main(String[] args) {
        short s = 5;
        s = s + 10;
        System.out.println(s);
    }
}

class MessageService {
    public void sendMessage() {
        System.out.println("Sending default message.");
    }
}

class EmailService extends MessageService {
    @Override
    public static void sendMessage() { // Attempting to override instance method as static
        System.out.println("Sending email message.");
    }
}

public class DataTypeChallenge {
    public static void main(String[] args) {
        double d = 0.0;
        int i = 0;
        try {
            System.out.println(1.0 / d);
            System.out.println(1 / i);
        } catch (ArithmeticException e) {
            System.out.println("Integer Division by Zero");
        }
    }
}

import java.util.TreeMap;

public class Test {
    public static void main(String[] args) {
        TreeMap<String, String> map = new TreeMap<>();
        map.put("key1", "value1");
        map.put(null, "value2");
        System.out.println(map.size());
    }
}

class SharedCounter {
    public int count = 0;
}

class Incrementer implements Runnable {
    private SharedCounter shared;
    public Incrementer(SharedCounter shared) {
        this.shared = shared;
    }
    @Override
    public void run() {
        for (int i = 0; i < 1000; i++) {
            shared.count++;
        }
    }
}

public class Main {
    public static void main(String[] args) throws InterruptedException {
        SharedCounter counter = new SharedCounter();
        Thread t1 = new Thread(new Incrementer(counter));
        Thread t2 = new Thread(new Incrementer(counter));
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("Final count: " + counter.count);
    }
}

interface Greeter {
    void greet(String name);
}

public class LambdaTest {
    public static void main(String[] args) {
        Greeter simpleGreeter = (name) -> {
            String message = "Hello, " + name + "!";
            System.out.println(message);
        };
        simpleGreeter.greet("World");
    }
}

import java.util.ArrayDeque;
import java.util.Deque;

public class QueueError {
    public static void main(String[] args) {
        Deque<String> deque = new ArrayDeque<>();
        deque.push("First");
        deque.push(null); // ArrayDeque does not permit nulls
    }
}

import java.io.*;

class Employee implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private int age;
    private transient String computedField;

    public Employee(String name, int age) {
        this.name = name;
        this.age = age;
        this.computedField = name + "_" + age;
    }

    public String toString() {
        return "Name: " + name + ", Age: " + age + ", Computed: " + computedField;
    }

    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        ois.defaultReadObject();
        this.computedField = name + "_reconstructed_" + age;
    }
}

public class SerializationTest {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Employee emp = new Employee("Alice", 30);
        System.out.println("Original: " + emp);

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(emp);
        oos.close();

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        Employee deserializedEmp = (Employee) ois.readObject();
        ois.close();

        System.out.println("Deserialized: " + deserializedEmp);
    }
}

public class Main {
    public void someMethod() {
        String data = "initial"; // This variable is not final or effectively final
        
        class LocalCustomException extends Exception {
            public LocalCustomException(String msg) {
                super(msg + data); // Accessing non-final 'data' - This line causes the compilation error
            }
        }
        try { new LocalCustomException("Error:"); } catch (LocalCustomException e) {}
    }

    public static void main(String[] args) {
        new Main().someMethod();
    }
}

import java.io.*;

class ExternalizableClass implements Externalizable {
    private static final long serialVersionUID = 1L;
    private String field1;
    private int field2;
    private transient String field3 = "Should not appear";

    public ExternalizableClass() {
        System.out.println("ExternalizableClass constructor called.");
    }
    
    public ExternalizableClass(String f1, int f2, String f3) {
        this.field1 = f1;
        this.field2 = f2;
        this.field3 = f3;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeObject(field1);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        System.out.println("readExternal called.");
        this.field1 = (String) in.readObject();
    }

    public String toString() {
        return "F1: " + field1 + ", F2: " + field2 + ", F3: " + field3;
    }
}

public class SerializationTest {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        ExternalizableClass obj = new ExternalizableClass("Alpha", 123, "Beta");
        
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(obj);
        oos.close();

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        ExternalizableClass deserializedObj = (ExternalizableClass) ois.readObject();
        ois.close();

        System.out.println(deserializedObj);
    }
}

public class MyClass {
    public static void main(String[] args) {
        char grade = 'A';
        switch (grade) {
            case 'A':
                System.out.println("Excellent");
                break;
            case 70000: // 70000 is beyond char's max value (65535)
                System.out.println("Invalid Grade");
                break;
            default:
                System.out.println("Pass");
        }
    }
}

public class Main {
    public static void main(String[] args) {
        int age = 25;
        System.out.println(age);
    }
}

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

public class DataProcessor {
    private int data;

    public DataProcessor(int value) {
        if (value < 0) {
            throw new InvalidInputException("Input must be non-negative.");
        }
        this.data = value;
    }

    public int getData() {
        return data;
    }
}

public class Main {
    public static void main(String[] args) {
        DataProcessor processor = new DataProcessor(-10);
        System.out.println(processor.getData());
    }
}