☕ Java MCQ Questions – Page 5

public class StaticWaitError {
    public static void staticWaitMethod() throws InterruptedException {
        // Attempting to wait() on the class object without holding its monitor
        StaticWaitError.class.wait();
    }

    public static void main(String[] args) {
        try {
            staticWaitMethod();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}

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(30);
        set.remove("20");
        System.out.println(set.size());
    }
}

public class DataTypeCharError {
    public static void main(String[] args) {
        char letter = 'AB';
        System.out.println(letter);
    }
}

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

public class AccessController {
    public void checkAccess(String user) throws RestrictedAccessException {
        if (!user.equals("admin")) {
            throw new RestrictedAccessException("Access denied for user: " + user);
        }
        System.out.println("Access granted for " + user);
    }

    public static void main(String[] args) {
        // Won't compile
    }
}

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

public class Main {
    public static void main(String[] args) {
        List<Character> charList = new ArrayList<>();
        charList.add('a');
        charList.remove(0);
        charList.remove(0); // Attempt to remove from an empty list
        System.out.println(charList);
    }
}

public class DaemonThreadConfig {
    public static void main(String[] args) {
        Thread t = new Thread(() -> {
            System.out.println("Child thread running. Is Daemon: " + Thread.currentThread().isDaemon());
        });
        t.start();
        t.setDaemon(true); // Attempt to set daemon status after starting
    }
}

public class Main {
    public static void main(String[] args) {
        String valueStr = "hello";
        Integer numberObj = Integer.valueOf(valueStr);
        System.out.println(numberObj);
    }
}

import java.io.BufferedReader;
import java.io.StringReader;
import java.io.IOException;

public class MyClass {
    public void readFile() {
        BufferedReader br = new BufferedReader(new StringReader("data"));
        String line = br.readLine();
    }
    public static void main(String[] args) {
        // Code here, if any, is not relevant to the error in readFile()
    }
}

import java.io.File;
import java.io.IOException;

public class FileTest {
    public static void main(String[] args) {
        File file = new File("temp_file_q5.txt");
        try {
            boolean created = file.createNewFile();
            System.out.println(created + " " + file.exists());
        } catch (IOException e) {
            System.out.println("Error");
        } finally {
            file.delete(); // Clean up
        }
    }
}

public class Test {
    public static void main(String[] args) {
        myIfStatement: if (true) {
            System.out.println("Inside the if block.");
            break myIfStatement;
        }
        System.out.println("After the if block.");
    }
}

import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;

public class LambdaCapture {
    public static void main(String[] args) {
        AtomicInteger counter = new AtomicInteger(10);
        Supplier<Integer> supplier = () -> {
            counter.incrementAndGet();
            return counter.get();
        };
        counter.set(5);
        System.out.println(supplier.get());
    }
}

public class LoopTest {
    public static void main(String[] args) {
        int k = 0;
        do {
            k++;
        } while (k < 3);
        System.out.print(k);
    }
}

class Product {
    private String name = "Laptop";
    // No public getter method for 'name'
}

public class Shop {
    public static void main(String[] args) {
        Product item = new Product();
        String productName = item.getName();
        System.out.println(productName);
    }
}

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockTest {
    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private String data = "initial";

    public String read() {
        rwLock.readLock().lock();
        try { Thread.sleep(10); return data; }
        catch (InterruptedException e) { Thread.currentThread().interrupt(); return null; }
        finally { rwLock.readLock().unlock(); }
    }

    public void write(String newData) {
        rwLock.writeLock().lock();
        try { Thread.sleep(50); this.data = newData; }
        catch (InterruptedException e) { Thread.currentThread().interrupt(); }
        finally { rwLock.writeLock().unlock(); }
    }

    public static void main(String[] args) throws InterruptedException {
        ReadWriteLockTest test = new ReadWriteLockTest();
        Thread r1 = new Thread(() -> System.out.println("R1 got: " + test.read()), "Reader-1");
        Thread r2 = new Thread(() -> System.out.println("R2 got: " + test.read()), "Reader-2");
        Thread w1 = new Thread(() -> test.write("updated"), "Writer-1");

        r1.start(); r2.start();
        Thread.sleep(5); // Give readers a slight head start
        w1.start();
        r1.join(); r2.join(); w1.join();
        System.out.println("Final data: " + test.data);
    }
}

import java.util.TreeSet;
import java.util.Set;

public class Test {
    public static void main(String[] args) {
        TreeSet<Integer> set = new TreeSet<>();
        set.add(10); set.add(20); set.add(30); set.add(40); set.add(50);
        Set<Integer> head = set.headSet(30); 
        Set<Integer> tail = set.tailSet(40, false); 
        System.out.println(head + " " + tail);
    }
}