☕ Java MCQ Questions – Page 112

public class MyJob implements Runnable {
    @Override
    public void run() {
        System.out.println("Job executed.");
    }

    public static void main(String[] args) {
        MyJob job = new MyJob();
        job.run();
        System.out.println("Main thread finished.");
    }
}

import java.util.Date;

class UserSession {
    private Date loginTime;
    public UserSession(Date loginTime) {
        this.loginTime = loginTime; 
    }
    public Date getLoginTime() {
        return loginTime;
    }
}

public class Main {
    public static void main(String[] args) {
        Date userLoginDate = new Date(1678886400000L); // March 15, 2023 00:00:00 GMT
        UserSession session = new UserSession(userLoginDate);
        System.out.println("Initial: " + session.getLoginTime().getTime());
        userLoginDate.setTime(1678972800000L); // March 16, 2023 00:00:00 GMT
        System.out.println("After modification: " + session.getLoginTime().getTime());
    }
}

public class Main {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("ABC");
        char c = sb.charAt(3);
        System.out.println(c);
    }
}

interface MyInterface {
    void method1();
    void method2();
}

public class Test {
    public static void main(String[] args) {
        MyInterface mi = () -> System.out.println("Hello");
    }
}

public class OperatorChallenge {
    public static void main(String[] args) {
        double d1 = 0.0 / 0.0;
        double d2 = 1.0 / 0.0;
        System.out.println(d1 == d1);
        System.out.println(d1 != d1);
        System.out.println(d2 + 1 == d2);
    }
}

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

public class IteratorError {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Item1");
        Iterator<String> it = list.iterator();
        it.remove(); // Calling remove() before next()
    }
}

public class DataTypeLongError {
    public static void main(String[] args) {
        long bigNumber = 2147483648;
        System.out.println(bigNumber);
    }
}

public class Light {
    private boolean isOn;

    public Light() {
        this.isOn = false;
    }

    public void toggle() {
        this.isOn = !this.isOn;
    }

    public boolean getStatus() {
        return isOn;
    }

    public static void main(String[] args) {
        Light livingRoomLight = new Light();
        livingRoomLight.toggle();
        livingRoomLight.toggle();
        livingRoomLight.toggle();
        System.out.println(livingRoomLight.getStatus());
    }
}

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

public class QueueError {
    public static void main(String[] args) {
        Queue<String> tasks = new LinkedList<>();
        String nextTask = tasks.poll();
        System.out.println(nextTask.length());
    }
}

// No import for FileReader
public class FileReaderIssue {
    public static void main(String[] args) throws java.io.IOException {
        FileReader reader = new FileReader("test.txt");
        int data = reader.read();
        reader.close();
    }
}

public class ArrayDeclarationError {
    public static void main(String[] args) {
        // Illegal combination of explicit size and initializer list
        int[] numbers = new int[3] {1, 2, 3};
        
        System.out.println(numbers[0]);
    }
}

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        ArrayList<Integer> nums = new ArrayList<>();
        nums.add(1);
        nums.add(2);
        nums.add(3);
        System.out.println(nums.size());
        nums.clear();
        System.out.println(nums.isEmpty());
    }
}

class Point {
    int x;
    int y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }
}

public class Main {
    public static void modifyPoint(Point p) {
        p.x = 100;
        p.y = 200;
        p = new Point(500, 600); // This reassigns the local parameter 'p'
    }

    public static void main(String[] args) {
        Point myPoint = new Point(10, 20);
        modifyPoint(myPoint);
        System.out.println("x: " + myPoint.x + ", y: " + myPoint.y);
    }
}

import java.util.HashSet;

public class Test {
    public static void main(String[] args) {
        HashSet<Integer> numbers = new HashSet<>();
        System.out.println(numbers.isEmpty());
        numbers.add(100);
        System.out.println(numbers.isEmpty());
    }
}

import java.util.HashSet;

class InconsistentKey {
    int id;
    public InconsistentKey(int id) { this.id = id; }
    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        InconsistentKey that = (InconsistentKey) o;
        return id == that.id;
    }
    @Override public int hashCode() { return System.identityHashCode(this); } // Inconsistent hash
}

public class Main {
    public static void main(String[] args) {
        HashSet<InconsistentKey> set = new HashSet<>();
        set.add(new InconsistentKey(5));
        set.add(new InconsistentKey(5));
        System.out.println(set.size());
    }
}

public class ArrayError {
    public static void main(String[] args) {
        String[][] words = new Object[2][2];
        System.out.println(words[0][0]);
    }
}

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

public class FileWriterNonExistentDir {
    public static void main(String[] args) {
        String filename = "nonexistent_dir/test.txt";
        try (FileWriter fw = new FileWriter(filename)) {
            fw.write("Hello");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        } finally {
            try { Files.deleteIfExists(Path.of(filename)); } catch (IOException ignored) {}
            try { Files.deleteIfExists(Path.of("nonexistent_dir")); } catch (IOException ignored) {}
        }
    }
}

public class Main {
    public static void main(String[] args) {
        boolean b = true;
        int i = (int) b;
        System.out.println(i);
    }
}