☕ Java MCQ Questions – Page 81

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

public class FileReaderTest {
    public static void main(String[] args) {
        // Assume test.txt exists and contains a single character 'A'
        char[] buffer = new char[3];
        try (FileReader reader = new FileReader("test.txt")) {
            int charsRead = reader.read(buffer); 
            int nextCharsRead = reader.read(buffer); 
            System.out.print(charsRead + ", " + nextCharsRead);
        } catch (IOException e) {
            System.out.print("Error");
        }
    }
}

abstract class Device {
    void powerOn() {
        System.out.println("Device is ON.");
    }
    abstract void operate();
}

class Phone extends Device {
    @Override
    void operate() {
        System.out.println("Dialing number.");
    }
}

public class Test {
    public static void main(String[] args) {
        Phone myPhone = new Phone();
        myPhone.powerOn();
    }
}

import java.util.LinkedList;
import java.util.Queue;

public class QueueOperations {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        queue.offer("Apple");
        queue.offer("Banana");
        System.out.println(queue.poll());
        queue.offer("Cherry");
        System.out.println(queue.peek());
    }
}

import java.io.*;

class NonSerializableClass {
    private String data = "secret data";
    public String getData() { return data; }
}

class Container implements Serializable {
    private String id;
    private NonSerializableClass nonSerializableField;

    public Container(String id, NonSerializableClass nonSerializableField) {
        this.id = id;
        this.nonSerializableField = nonSerializableField;
    }
}

public class Test {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        try {
            Container container = new Container("C1", new NonSerializableClass());
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            oos.writeObject(container);
            oos.close();
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

public class LoopError {
    public static void main(String[] args) {
        for (int i = 0; i < 3; int j = 0) {
            System.out.println(i);
        }
    }
}

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

public class Main {
    public static void main(String[] args) {
        List<String> words = new ArrayList<>();
        words.add("hello");
        words.add("world");
        Iterator<String> it1 = words.iterator();
        it1.next(); // "hello"
        words.add("java"); // Modifies the list directly, outside the iterator's control
        it1.next(); // Attempts to iterate further after modification
    }
}

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

public class InfiniteLoopMemory {
    public static void main(String[] args) {
        List<byte[]> data = new ArrayList<>();
        int i = 0;
        while (true) {
            data.add(new byte[1024 * 1024]); // Allocate 1MB
            i++;
            System.out.println("Allocated " + i + "MB");
        }
    }
}

import java.io.*;

class MyObject implements Serializable {
    private String name;
    public MyObject(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
}

public class Test {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        MyObject obj = new MyObject("Hello Serialization");
        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);
        MyObject deserializedObj = (MyObject) ois.readObject();
        ois.close();
        System.out.println(deserializedObj.getName());
    }
}

public class MyClass {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("abcdefg");
        sb.delete(2, 5);
        System.out.print(sb);
    }
}

import java.io.IOException;

class Reader {
    public void readData() throws IOException {
        System.out.println("Reading data...");
    }
}

class FileReader extends Reader {
    @Override
    public void readData() throws Exception { // Broadening checked exception
        System.out.println("Reading file data...");
    }
}

public class ThreadStateDemo8 {
    private static final Object monitor = new Object();
    public static void main(String[] args) throws InterruptedException {
        Thread t = new Thread(() -> {
            synchronized (monitor) {
                try {
                    System.out.println("Thread is waiting indefinitely.");
                    monitor.wait(); // Stays in WAITING state
                    System.out.println("Thread resumed.");
                } catch (InterruptedException e) {
                    System.out.println("Thread interrupted while waiting.");
                }
            }
        });
        t.start();
        Thread.sleep(100); // Give thread time to enter wait()
        System.out.println("State of t: " + t.getState());
        Thread.sleep(200); // Wait longer, no notify() is called
        System.out.println("State of t after more time: " + t.getState());
    }
}

abstract class Shape {
    public abstract void draw();
}

class Circle extends Shape {
    @Override
    public void draw() {
        System.out.print("Drawing a circle");
    }
}

public class Main {
    public static void main(String[] args) {
        Shape s = new Circle();
        s.draw();
    }
}

class Parent {
    public void init() {
        System.out.println("Initializing Parent");
    }
}

class Child extends Parent {
    @Override
    public void init(String config) {
        System.out.println("Initializing Child with config: " + config);
    }
}