☕ Java MCQ Questions – Page 138

public class Main {
    public static void main(String[] args) {
        Thread t = new Thread(() -> System.out.println("Worker thread."));
        try {
            t.setPriority(Thread.MAX_PRIORITY + 1); // Invalid priority
        } catch (SecurityException e) {
            System.out.println("Security Exception");
        }
        t.start();
    }
}

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        ArrayList<String> colors = new ArrayList<>();
        colors.add("Red");
        colors.add("Green");
        colors.add("Blue");
        colors.remove(0);
        System.out.println(colors.get(0));
    }
}

public class SwitchTest {
    public static void main(String[] args) {
        char code = 'C';
        String description = "";
        switch (code) {
            case 'A':
            case 'E':
            case 'I':
                description = "Vowel";
                break;
            case 'O':
                description = "Round Vowel";
                break;
            case 'U':
                description = "Long Vowel";
                break;
            default:
                description = "Consonant";
        }
        System.out.println(description);
    }
}

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

public class FileReaderTest {
    public static void main(String[] args) {
        // Assume test.txt exists and contains a single character 'Z'
        File file = new File("test.txt");
        try (FileReader reader = new FileReader(file)) {
            int charCode = reader.read();
            System.out.print((char) charCode);
        } catch (IOException e) {
            System.out.print("Error");
        }
    }
}

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class TestClass {
    public static void main(String[] args) {
        BufferedReader br; 
        try (br = new BufferedReader(new FileReader("input.txt"))) {
            String line = br.readLine();
            System.out.println(line);
        } catch (IOException e) {
            System.err.println("Error: " + e.getMessage());
        }
    }
}

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

final class MyImmutableList {
    private final List<String> data;
    public MyImmutableList(List<String> data) {
        this.data = new ArrayList<>(data); // Defensive copy
    }
    public List<String> getData() {
        return new ArrayList<>(data); // Defensive copy
    }
}

public class Main {
    public static void main(String[] args) {
        List<String> mutableList = new ArrayList<>();
        mutableList.add("A");
        MyImmutableList immutableList = new MyImmutableList(mutableList);
        mutableList.add("B"); // Modify original list
        immutableList.getData().add("C"); // Modify returned copy
        System.out.println(immutableList.getData().size());
    }
}

import java.util.HashSet;

public class Test {
    public static void main(String[] args) {
        HashSet<Character> chars = new HashSet<>();
        chars.add('A');
        chars.add('B');
        chars.add('C');
        chars.remove('B');
        System.out.println(chars.size());
    }
}

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

public class FileWriterToDirectory {
    public static void main(String[] args) {
        String dirname = "my_directory";
        File dir = new File(dirname);
        try {
            Files.createDirectory(Path.of(dirname));
            try (FileWriter fw = new FileWriter(dir)) {
                fw.write("This should fail.");
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        } finally {
            try { Files.deleteIfExists(Path.of(dirname)); } catch (IOException ignored) {}
        }
    }
}

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

public class Main {
    public static void main(String[] args) {
        MyRunnable r = new MyRunnable();
        Thread t = new Thread(r);
        t.start();
        t.start(); // Second call to start()
    }
}

import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;

public class Test {
    public static void main(String[] args) {
        Map<String, Integer> counts = new HashMap<>();
        counts.put("apple", 10);
        
        // Attempt to merge with a null remapping function
        // when both old and new values are non-null
        counts.merge("apple", 5, null); 
        System.out.println(counts.get("apple"));
    }
}

import java.util.function.Supplier;

class Product {
    String name;
    public Product() { this.name = "Default Product"; }
    public Product(String name) { this.name = name; }
}

public class ConstructorReference {
    public static void main(String[] args) {
        Supplier<Product> productSupplier = Product::new; // References no-arg constructor
        Product p = productSupplier.get();
        System.out.println(p.name);
    }
}

import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> immutableColors = List.of("Cyan", "Magenta", "Yellow");
        immutableColors.add("Black"); // Attempt to add to an immutable list
        System.out.println(immutableColors);
    }
}