☕ Java MCQ Questions – Page 149

class SuperClass {
    String message = "Hello from Super";
}

class SubClass extends SuperClass {
    String message = "Hello from Sub";
}

public class Main {
    public static void main(String[] args) {
        SuperClass ref = new SubClass();
        System.out.print(ref.message);
    }
}

import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<String> items = new LinkedList<>();
        items.add("Pen");
        items.add("Pencil");
        items.add("Eraser");
        items.remove("Pencil");
        System.out.println(items.size());
    }
}

public class BuilderError {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Java");
        sb.setCharAt(4, '!');
        System.out.println(sb);
    }
}

import java.io.*;

class Configuration implements Serializable {
    private String setting1;
    private transient String setting2; // Will not be serialized

    public Configuration(String s1, String s2) {
        this.setting1 = s1;
        this.setting2 = s2;
    }

    public String getInfo() {
        return "Setting 1: " + setting1 + ", Setting 2 length: " + setting2.length();
    }
}

public class SerializationQuestion8 {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Configuration config = new Configuration("ValueA", "ValueB");
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("config.ser"))) {
            oos.writeObject(config);
        }

        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("config.ser"))) {
            Configuration loadedConfig = (Configuration) ois.readObject();
            System.out.println(loadedConfig.getInfo()); // This line will cause an error
        }
    }
}

class Item {
    final String name;
    final int id;

    Item() {
        this.name = "Default";
    }
}

public class Main {
    public static void main(String[] args) {
        long l = 20000000000L; // 20 billion
        int i = l;
        System.out.println(i);
    }
}

public class StringError {
    public static void main(String[] args) {
        String data = "item1";
        String[] parts = data.split(",");
        System.out.println(parts[1]);
    }
}

public class Q7_JoinTimeoutState {
    public static void main(String[] args) throws InterruptedException {
        Thread worker = new Thread(() -> {
            try {
                Thread.sleep(500); // Takes long time
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        });
        worker.start();
        Thread.sleep(10); // Ensure worker started
        
        System.out.println("Worker state before join: " + worker.getState());
        worker.join(100); // Main thread waits for max 100ms
        System.out.println("Worker state after join with timeout: " + worker.getState());
        System.out.println("Main thread continues.");
        worker.join(); // Main thread waits indefinitely now for worker to finish
        System.out.println("Worker state after final join: " + worker.getState());
    }
}

import java.io.*;

class ClassContainer implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private Class<?> type; // Field of type Class, which is not Serializable

    public ClassContainer(String name, Class<?> type) {
        this.name = name;
        this.type = type;
    }

    public Class<?> getType() { return type; }
}

public class SerializationError7 {
    public static void main(String[] args) throws IOException {
        ClassContainer container = new ClassContainer("String Type", String.class);
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(container); // Error occurs here
        oos.close();
    }
}

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

public class Main {
    public static void main(String[] args) throws IOException {
        StringWriter sw = new StringWriter();
        BufferedWriter bw = new BufferedWriter(sw, 4); // Small buffer for demonstration
        bw.write('1');
        bw.write('2');
        bw.write('3');
        bw.write('4');
        bw.write('5');
        bw.close();
        System.out.print(sw.toString());
    }
}

public class Main {
    public static void main(String[] args) {
        int x = 10;
        if (x > 5) {
            continue;
        }
        System.out.println("Hello");
    }
}

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

public class Main {
    public static void main(String[] args) throws IOException {
        StringWriter sw = new StringWriter();
        BufferedWriter bw = new BufferedWriter(sw);
        char[] chars = {'A', 'B', 'C', 'D', 'E'};
        bw.write(chars, 1, 3); // Writes 'BCD'
        bw.write("Testing", 0, 2); // Writes 'Te'
        bw.close();
        System.out.print(sw.toString());
    }
}

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

public class FileReaderPermission {
    public static void main(String[] args) {
        // Assume 'protected.txt' exists but has no read permissions
        String fileName = "protected.txt";
        try (FileReader reader = new FileReader(new File(fileName))) {
            System.out.println("File opened successfully.");
            reader.read(); 
        } catch (IOException e) {
            String msg = e.getMessage();
            if (msg != null && (msg.contains("Permission denied") || msg.contains("Access is denied"))) {
                System.out.println("Error: Permission denied.");
            } else if (msg != null && msg.contains("No such file or directory")) {
                System.out.println("Error: File not found.");
            } else {
                System.out.println("Error: An unexpected I/O error occurred: " + msg);
            }
        }
    }
}

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Set<String> set = Collections.singleton("initial");
        set.add("another"); // Attempt to modify singleton set
    }
}