☕ Java MCQ Questions – Page 76

public class StringTest {
    public static void main(String[] args) {
        String val = null;
        System.out.println(String.valueOf(val) + ".isEmpty:" + (val != null && val.isEmpty()));
    }
}

abstract class Shape {
    abstract double getArea();
    abstract double getPerimeter();
}

class Circle extends Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    double getArea() {
        return Math.PI * radius * radius;
    }
}

import java.util.function.Consumer;

class Printer {
    public void print(String s) {
        System.out.println("String: " + s);
    }
    public void print(Object o) {
        System.out.println("Object: " + o.getClass().getName());
    }
}

public class MethodRefTest {
    public static void main(String[] args) {
        Printer p = new Printer();
        Consumer<String> consumer = p::print;
        consumer.accept("Test");
    }
}

public class ArrayError {
    public static void main(String[] args) {
        int[] numbers;
        // The array reference 'numbers' is not explicitly initialized here
        System.out.println(numbers.length);
    }
}

public class EffectivelyFinal {
    public static void main(String[] args) {
        int count = 0;
        Runnable r = new Runnable() {
            @Override
            public void run() {
                System.out.println(count); // Accesses count
            }
        };
        count = 1; // This line causes the error
        r.run();
    }
}

import java.util.function.Function;

public class Test {
    public static void main(String[] args) {
        Function<String, Integer> stringLength = String::length;
        Function<Integer, String> intToString = String::valueOf;

        int length = stringLength.apply("Java");
        String result = intToString.apply(length);
        System.out.println(result + result.length());
    }
}

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

public class UnmodifiableListRemove {
    public static void main(String[] args) {
        List<String> originalList = new ArrayList<>(Arrays.asList("P", "Q", "R"));
        List<String> unmodifiableList = Collections.unmodifiableList(originalList);
        Iterator<String> iterator = unmodifiableList.iterator();
        iterator.next(); // Moves past P
        iterator.remove(); // Attempts to remove P
        System.out.println(unmodifiableList);
    }
}

class Super {
    Number getObject() {
        return Integer.valueOf(10);
    }
}

class Sub extends Super {
    String getObject() { // Line 8
        return "Hello";
    }
}

public class Main {
    public static void main(String[] args) {
        Super s = new Sub();
        System.out.println(s.getObject());
    }
}

import java.io.*;

class Item implements Serializable {
    String itemName;
    int itemId;
    public Item(String itemName, int itemId) {
        this.itemName = itemName;
        this.itemId = itemId;
    }
    @Override
    public String toString() {
        return itemName + ":" + itemId;
    }
}

class Box implements Serializable {
    Item item1;
    Item item2; // This will be null
    public Box(Item item1, Item item2) {
        this.item1 = item1;
        this.item2 = item2;
    }
    @Override
    public String toString() {
        return "Box[" + item1 + "," + item2 + "]";
    }
}

public class Test {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Item i1 = new Item("Laptop", 101);
        Box box = new Box(i1, null); // item2 is null

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

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        Box deserializedBox = (Box) ois.readObject();
        ois.close();
        System.out.println(deserializedBox.toString());
    }
}

import java.util.ArrayList;
import java.util.Collection;

class Item {
    int id;
    String name;
    public Item(int id, String name) {
        this.id = id;
        this.name = name;
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Item item = (Item) o;
        return id == item.id && name.equals(item.name);
    }
    @Override
    public int hashCode() {
        return java.util.Objects.hash(id, name);
    }
    @Override
    public String toString() {
        return "Item{" + id + "}";
    }
}

public class Test {
    public static void main(String[] args) {
        ArrayList<Item> list1 = new ArrayList<>();
        list1.add(new Item(1, "Apple"));
        list1.add(new Item(2, "Banana"));
        list1.add(new Item(3, "Cherry"));

        ArrayList<Item> list2 = new ArrayList<>();
        list2.add(new Item(2, "Banana")); 
        list2.add(new Item(4, "Date"));

        list1.removeAll(list2);
        System.out.println(list1);
    }
}

class Base {
    private void secretMethod() {
        System.out.println("Base's secret");
    }
}

class Derived extends Base {
    @Override
    public void secretMethod() {
        System.out.println("Derived's secret");
    }
}

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

public class QueueTest {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        String result = "";
        try {
            result += queue.poll() + ",";
            result += queue.peek() + ",";
            result += queue.remove() + ",";
        } catch (Exception e) {
            result += e.getClass().getSimpleName();
        }
        System.out.println(result);
    }
}