☕ Java MCQ Questions – Page 103

import java.util.Comparator;
import java.util.PriorityQueue;

class MyData {}

public class QError10 {
    public static void main(String[] args) {
        Comparator<String> stringComparator = (s1, s2) -> s1.compareTo(s2);
        PriorityQueue<MyData> pq = new PriorityQueue<>(stringComparator);
        pq.add(new MyData());
        System.out.println(pq.poll());
    }
}

import java.io.BufferedWriter;
import java.io.FileWriter;

public class Main {
    public static void main(String[] args) {
        BufferedWriter bw = null;
        try {
            bw = new BufferedWriter(new FileWriter("output.txt"));
            bw.write("Data to write.");
        } catch (Exception e) {
            e.printStackTrace();
        }
        // close() method can throw IOException and is outside a try-catch block
        bw.close();
    }
}

public class ImmutableStringExample {
    public static void main(String[] args) {
        final String message = "Hello";
        message = "World"; // Attempt to reassign final variable
        System.out.println(message);
    }
}

public class DataTypeBooleanError {
    public static void main(String[] args) {
        boolean isValid = 1;
        System.out.println(isValid);
    }
}

import java.util.function.BiFunction;

class MathUtils {
    public static int multiply(int a, int b) {
        return a * b;
    }
}

public class MethodRefTest {
    public static void main(String[] args) {
        BiFunction<Integer, Integer, Integer> multiplier = MathUtils::multiply;
        int result = multiplier.apply(5, 3);
        System.out.println("Result: " + result);
    }
}

public class TypeOrder {
    void process(int num, String text) {
        System.out.println("Int-String: " + num + " " + text);
    }
    void process(String text, int num) {
        System.out.println("String-Int: " + text + " " + num);
    }
    public static void main(String[] args) {
        TypeOrder to = new TypeOrder();
        to.process(10, "Hello");
        to.process("World", 20);
    }
}

import java.io.BufferedWriter;
import java.io.StringWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        StringWriter stringWriter = new StringWriter();
        try (BufferedWriter writer = new BufferedWriter(stringWriter)) {
            writer.append("First");
            writer.append(' ');
            writer.append("Second");
            writer.flush();
            System.out.print(stringWriter.toString());
        } catch (IOException e) {
            System.out.print("Error");
        }
    }
}

public class MyClass {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Start");
        sb.append("End").insert(5, "Middle");
        System.out.print(sb);
    }
}

public class LoopTest {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30};
        int i = 0;
        while (i <= numbers.length) {
            System.out.println(numbers[i]);
            i++;
        }
    }
}

class Person {
    protected String name = "Default";
}

class Student extends Person {
    void displayName() {
        System.out.println("Name: " + name);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s = new Student();
        s.displayName();
    }
}

abstract class Gadget {
    public abstract void activate();
    public void status() { System.out.println("Gadget OK"); }
}

class Smartwatch extends Gadget { // Missing implementation of activate()
    @Override
    public void status() { System.out.println("Smartwatch Ready"); }
}

public class WhileLoopDemo {
    public static void main(String[] args) {
        int k = 3;
        while (k > 0) {
            System.out.print(k);
            k--;
        }
    }
}

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

public class Test {
    public static void main(String[] args) {
        Set<String> set = new TreeSet<>();
        set.add("hello");
        set.add("world");
        try {
            set.add(null);
            System.out.println(set);
        } catch (NullPointerException e) {
            System.out.println("NullPointerException caught!");
        }
    }
}

public class ConditionalCompileError {
    public static void main(String[] args) {
        final boolean FLAG = true;
        if (FLAG) {
            System.out.println("Condition is true.");
        } else { // This 'else' branch is unreachable.
            System.out.println("Condition is false.");
        }
    }
}

import java.io.FileReader;
import java.io.FileNotFoundException;

public class FileReaderIssue {
    public static void main(String[] args) throws FileNotFoundException {
        FileReader reader = new FileReader("existing.txt"); // Assume existing.txt exists
        // ... some operations ...
        reader.close(); // Potential IOException, not declared or caught
    }
}

import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        TreeSet<String> names = new TreeSet<>();
        names.add("Alice");
        names.add("Bob");
        names.add(null);
    }
}