☕ Java MCQ Questions – Page 3

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

public class QueueIsEmpty {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        queue.offer("A");
        queue.offer("B");
        queue.poll();
        System.out.println(queue.isEmpty());
        queue.poll();
        System.out.println(queue.isEmpty());
    }
}

public class LambdaTest {
    public static void main(String[] args) {
        Runnable r = () -> System.out.println("Hello Lambda!");
        r.run();
    }
}

import java.io.File;

public class FileTest {
    public static void main(String[] args) {
        File directory = new File("nonExistentDir");
        System.out.println(directory.exists() + " " + directory.isDirectory());
    }
}

public class ArrayError {
    public static void main(String[] args) {
        int[][] jaggedArray = new int[2][];
        jaggedArray[0] = new int[]{1, 2};
        for (int i = 0; i < jaggedArray.length; i++) {
            for (int j = 0; j < jaggedArray[i].length; j++) {
                System.out.print(jaggedArray[i][j] + " ");
            }
        }
    }
}

public class ArrayError {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3};
        arr.length = 5;
        System.out.println(arr.length);
    }
}

class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Runnable running.");
    }
}

public class TestThread {
    public static void main(String[] args) {
        MyRunnable r = new MyRunnable();
        r.run();
        System.out.println("Main finished.");
    }
}

import java.io.*;

class FaultyReader extends Reader {
    private int count = 0;
    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        if (count++ > 0) { // Throws on second read attempt
            throw new IOException("Faulty Reader encountered an error!");
        }
        if (len == 0) return 0;
        cbuf[off] = 'A'; // Simulate reading one char
        return 1;
    }

    @Override
    public void close() throws IOException { /* Do nothing */ }
}

public class FaultyBufferedReaderTest {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FaultyReader())) {
            br.read(); // First read, okay
            br.readLine(); // Second read, underlying reader throws
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

public class SBError {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Initial: ");
        char[] chars = {'J', 'a', 'v', 'a'}; // Length 4
        // Try to append 5 characters starting from offset 0
        sb.append(chars, 0, 5);
        System.out.println(sb);
    }
}

class CustomException1 extends Exception { public CustomException1(String msg) { super(msg); } }
class CustomException2 extends Exception { public CustomException2(String msg) { super(msg); } }
public class Main {
    public static void methodA() throws CustomException1 { throw new CustomException1("Problem from A"); }
    public static void main(String[] args) {
        try { methodA(); }
        catch (CustomException1 e) {
            System.out.println("Caught CE1: " + e.getMessage());
            try { throw new CustomException2("Problem from Catch1"); }
            catch (CustomException2 ce2) { System.out.println("Caught CE2: " + ce2.getMessage()); }
        } catch (Exception e) { System.out.println("Caught general: " + e.getMessage()); }
        finally { System.out.println("Finally executed."); }
    }
}

public class Test {
    public static void main(String[] args) {
        String result = "";
        outer: for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (i == 1 && j == 1) {
                    break outer;
                }
                result += "(" + i + "," + j + ")";
            }
        }
        System.out.print(result);
    }
}

class InitOrder {
    { 
        System.out.println("Instance Initializer Block");
    }
    InitOrder() {
        System.out.println("Constructor");
    }
}
public class Main {
    public static void main(String[] args) {
        InitOrder obj = new InitOrder();
    }
}

import java.util.function.Function;

class Box<T> {
    T item;
    public Box(T item) { this.item = item; }
    @Override public String toString() { return "Box(" + item + ")"; }
}

public class GenericConstructorRef {
    public static void main(String[] args) {
        Function<String, Box<String>> stringBoxCreator = Box::new;
        Box<String> stringBox = stringBoxCreator.apply("Hello");

        Function<Integer, Box<Integer>> intBoxCreator = Box::new;
        Box<Integer> intBox = intBoxCreator.apply(123);

        System.out.println(stringBox);
        System.out.println(intBox);
    }
}

import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Arrays;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<Character> chars = new LinkedList<>(Arrays.asList('a', 'b', 'c'));
        ListIterator<Character> it = chars.listIterator();
        it.next(); // Cursor after 'a'
        it.remove(); // Removes 'a'
        it.remove(); // Second remove without next/previous
        System.out.println(chars);
    }
}

public class Test {
    public static void main(String[] args) {
        String result = "";
        for (int i = 0; i < 3; i++) {
            try {
                if (i == 1) {
                    break;
                }
                result += i;
            } finally {
                result += "F";
            }
        }
        System.out.print(result);
    }
}