☕ Java MCQ Questions – Page 99

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

public class FileReaderEncoding {
    public static void main(String[] args) throws IOException {
        // Assume 'data.txt' has content: 'é' (UTF-8 encoded: 0xC3 0xA9)
        // Assume platform default encoding is ISO-8859-1
        StringBuilder sb = new StringBuilder();
        try (FileReader reader = new FileReader(new File("data.txt"))) {
            int c;
            while ((c = reader.read()) != -1) {
                sb.append((char) c);
            }
        }
        System.out.println(sb.toString());
    }
}

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

public class TestClass {
    public static void main(String[] args) {
        BufferedReader br = null;
        try {
            new FileReader("valid.txt"); // File exists, but not assigned to 'br'
            String line = br.readLine();
            System.out.println(line);
        } catch (IOException e) {
            System.err.println("IO Error");
        } catch (NullPointerException e) {
            System.err.println("NPE Caught: " + e.getMessage());
        }
    }
}

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

public class FileWriterAppendFileObject {
    public static void main(String[] args) {
        String filename = "append_file.txt";
        File file = new File(filename);
        try {
            try (FileWriter fw = new FileWriter(file)) { fw.write("First line.\n"); }
            try (FileWriter fw = new FileWriter(file, true)) { fw.write("Second line.\n"); }
            try (FileWriter fw = new FileWriter(file, false)) { fw.write("Third line."); }

            try (BufferedReader br = new BufferedReader(new FileReader(file))) {
                String line; while ((line = br.readLine()) != null) { System.out.println(line); }
            }
        } catch (IOException e) { System.out.println("Error: " + e.getMessage());
        } finally { try { Files.deleteIfExists(Path.of(filename)); } catch (IOException ignored) {} }
    }
}

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

public class Test {
    public static void main(String[] args) {
        Set<Integer> numbers = new TreeSet<>();
        numbers.add(5);
        numbers.add(2);
        numbers.add(8);
        numbers.add(1);
        System.out.println(numbers);
    }
}

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

public class PassMutable {
    public static void modifyList(List<String> list) {
        list.add("C++");
        System.out.println("Inside method: " + list);
    }

    public static void main(String[] args) {
        List<String> languages = new ArrayList<>();
        languages.add("Java");
        languages.add("Python");
        modifyList(languages);
        System.out.println("Outside method: " + languages);
    }
}

public class OverloadDemo8 {
    void showChar(int val) {
        System.out.println("Int value: " + val);
    }
    void showChar(char val) {
        System.out.println("Char value: " + val);
    }
    public static void main(String[] args) {
        OverloadDemo8 obj = new OverloadDemo8();
        obj.showChar('C');
    }
}

public class VarargsArrayConversion {
    public static void printArgs(String... args) {
        System.out.println("Number of args: " + args.length);
        for (String s : args) {
            System.out.print(s + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        String[] arr = {"hello", "world"};
        printArgs(arr);
        printArgs("java", "is", "fun");
        printArgs();
    }
}

enum Day { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY }

public class EnumSwitchExhaustiveError {
    public static void main(String[] args) {
        Day today = Day.MONDAY;
        String typeOfDay = switch (today) { // Error expected here
            case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY -> "Weekday";
            case SATURDAY -> "Weekend";
            // Missing SUNDAY
        };
        System.out.println(typeOfDay);
    }
}

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread started.");
        int x = 10 / 0; // This will cause an ArithmeticException
        System.out.println("Thread finished.");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.start();
    }
}

class Base {
    public Base() {
        System.out.println("Base constructor");
    }
}

class Derived extends Base {
    public Derived() {
        System.out.println("Derived constructor");
        super(); // Call to super() is not the first statement
    }
}

import java.util.PriorityQueue;
import java.util.Queue;

class CustomObject {}

public class QError2 {
    public static void main(String[] args) {
        Queue<CustomObject> pq = new PriorityQueue<>();
        pq.add(new CustomObject());
        pq.add(new CustomObject());
        System.out.println(pq.poll());
    }
}

interface A { default void show() { System.out.println("A"); } }
interface B { default void show() { System.out.println("B"); } }
interface C { void show(); }

class MyClass implements A, B, C {
    @Override
    public void show() {
        A.super.show();
        System.out.println("MyClass");
    }
}

public class Test {
    public static void main(String[] args) {
        new MyClass().show();
    }
}

public class StringError2 {
    public static void main(String[] args) {
        String text = "hello"; // Length is 5, valid indices are 0-4
        char c = text.charAt(5);
        System.out.println(c);
    }
}

import java.io.*;

public class BufferReadArrayError {
    public static void main(String[] args) {
        try (StringReader sr = new StringReader("Hello World");
             BufferedReader br = new BufferedReader(sr)) {
            char[] buffer = new char[5];
            // Invalid offset and length combination: off=3, len=3, buffer.length=5. off+len (6) > buffer.length
            br.read(buffer, 3, 3);
            System.out.println(new String(buffer));
        } catch (IndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IOException: " + e.getMessage());
        }
    }
}

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