Java MCQ Questions – Page 100 of 200

Q: What is the output of this code?

A) Start Inside Try Inside Finally End. The program starts, prints 'Start'. Then, the 'try' block executes, followed by the 'finally' block (since no exception occurs). Finally, the statement after the try-finally block executes.

Q: What is the output of this Java code snippet?

A) false. The `isAbsolute()` method tests whether this abstract pathname is absolute. 'myFile.txt' is a relative path, so `isAbsolute()` returns `false`.

Q: What is the output of this Java code snippet?

A) Alice and Bob. Two distinct `Person` objects are created, `p1` and `p2`, each with their own `name` instance variable initialized by the constructor. The code then prints the names from both objects.

Q: Consider an immutable class `MyImmutableClass` that holds a `private final Map internalMap;`. Which of the following is the most robust way to ensure that the `internalMap` remains immutable even when accessed via a getter?

B) Return `Collections.unmodifiableMap(internalMap)` from the getter.. `Collections.unmodifiableMap()` returns a view of the map that throws an `UnsupportedOperationException` if modification attempts are made, providing strong immutability guarantees for the returned object.

Q: Which method is used to add a sequence of characters to the end of an existing `StringBuffer` object?

C) append(). The `append()` method is specifically designed to add various types of data (strings, chars, ints, etc.) to the end of the `StringBuffer`.

Q: What is the output of this code?

A) 5. The array `grid` is initialized with default values of 0. `grid[0][0]` is set to 5. `grid[1][0]` remains its default value of 0. So, 5 + 0 = 5.

Q: What is the compilation error in the following Java code?

C) Type mismatch: cannot convert from String to int. A `String` literal cannot be directly assigned to an `int` variable without explicit conversion, leading to a type mismatch compilation error.

Q: What is the error encountered when compiling this Java code?

A) Compile-time error: Cannot create a generic array of T. Due to Java's type erasure, the runtime type of 'T' is not known. Therefore, it's not possible to create a generic array directly using `new T[size]` because the JVM needs to know the specific component type at array creation time. This results in a compile-time error.

Q: What is the output of this Java code?

A) Hello FileWriter. Although `flush()` is not explicitly called, the `close()` method of `FileWriter` (and its superclasses) automatically flushes any buffered data to the underlying stream or file before closing. Therefore, the written content will be persisted to the file and readable.

Q: Conceptually, how does a HashMap store its entries to handle collisions?

B) Using a linked list for each bucket, which can become a tree if the list is too long (Java 8+).. HashMap internally uses an array of buckets, where each bucket typically stores entries in a linked list. From Java 8, long linked lists are converted to Red-Black trees for performance.

Q1981 easy code output

What is the output of this code?

java

public class Main {
    public static void main(String[] args) {
        System.out.print("Start ");
        try {
            System.out.print("Inside Try ");
        } finally {
            System.out.print("Inside Finally ");
        }
        System.out.print("End ");
    }
}

Q1982 easy code output

What is the output of this Java code snippet?

java

import java.io.File;

public class FileTest {
    public static void main(String[] args) {
        File file = new File("myFile.txt");
        System.out.println(file.isAbsolute());
    }
}

Q1983 easy code output

What is the output of this Java code snippet?

java

class Person {
    String name;
    public Person(String name) {
        this.name = name;
    }
}
public class Main {
    public static void main(String[] args) {
        Person p1 = new Person("Alice");
        Person p2 = new Person("Bob");
        System.out.print(p1.name + " and " + p2.name);
    }
}

Q1984 hard

Consider an immutable class `MyImmutableClass` that holds a `private final Map<String, String> internalMap;`. Which of the following is the most robust way to ensure that the `internalMap` remains immutable even when accessed via a getter?

Q1985 easy

Which method is used to add a sequence of characters to the end of an existing `StringBuffer` object?

Q1986 easy code output

What is the output of this code?

java

public class Main {
    public static void main(String[] args) {
        int[][] grid = new int[2][3];
        grid[0][0] = 5;
        grid[1][2] = 10;
        System.out.println(grid[0][0] + grid[1][0]);
    }
}

Q1987 medium code error

What is the compilation error in the following Java code?

java

public class TypeMismatch {
    public static void main(String[] args) {
        int count = "ten";
        System.out.println(count);
    }
}

Q1988 hard code error

What is the error encountered when compiling this Java code?

java

import java.util.List;

public class GenericArrayError<T> {
    T[] createArray(int size) {
        return new T[size];
    }

    public static void main(String[] args) {
        GenericArrayError<String> creator = new GenericArrayError<>();
        String[] strArray = creator.createArray(5);
    }
}

Q1989 hard code output

What is the output of this Java code?

java

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 FileWriterImplicitFlush {
    public static void main(String[] args) {
        String filename = "implicit_flush_test.txt";
        try {
            FileWriter fw = new FileWriter(filename);
            fw.write("Hello FileWriter");
            fw.close(); 

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

Q1990 easy

Conceptually, how does a HashMap store its entries to handle collisions?

Q1991 easy code error

What kind of error will occur when compiling or running the following Java code snippet?

java

import java.io.File;

public class FileError6 {
    public static void main(String[] args) {
        File file = null;
        if (args.length > 0) {
            file = new File(args[0]);
        }
        file.delete(); // Potentially problematic line
        System.out.println("Operation attempted.");
    }
}

Q1992 hard code error

What is the result of executing this Java code snippet?

java

public class PrimitiveArrayCast {
    public static void main(String[] args) {
        int[] intArray = {1, 2, 3};
        Object[] objArray = (Object[]) intArray;
        System.out.println("Array cast successful");
    }
}

Q1993 medium code output

What is the output of this code?

java

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

public class PathResolution {
    public static void main(String[] args) throws IOException {
        File file = new File("./temp_data/../my_document.pdf");
        System.out.println(file.getAbsolutePath().contains("..") + ", " + file.getCanonicalPath().contains(".."));
    }
}

Q1994 hard code output

What is the final output of this code, specifically the `Barrier reached` lines and `sharedCounter` values?

java

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierTest {
    private final CyclicBarrier barrier;
    private int sharedCounter = 0;

    public CyclicBarrierTest() {
        this.barrier = new CyclicBarrier(3, () -> {
            System.out.println("Barrier reached! All threads arrived. Counter: " + sharedCounter);
            sharedCounter = 0; // Reset for next phase
        });
    }

    public void worker(String name) {
        try {
            Thread.sleep(50); synchronized(this){ sharedCounter++; } barrier.await();
            Thread.sleep(50); synchronized(this){ sharedCounter++; } barrier.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            Thread.currentThread().interrupt();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        CyclicBarrierTest test = new CyclicBarrierTest();
        for (int i = 0; i < 3; i++) {
            new Thread(() -> test.worker("Worker-" + i)).start();
        }
        Thread.sleep(1000); // Allow time for all phases
    }
}

Q1995 medium code output

What is the output of the following Java program?

java

public class TryCatchFinallyFlow {
    public static void main(String[] args) {
        try {
            System.out.println("1. Inside try");
            throw new RuntimeException("Test Exception");
        } catch (RuntimeException e) {
            System.out.println("2. Inside catch: " + e.getMessage());
        } finally {
            System.out.println("3. Inside finally");
        }
        System.out.println("4. After blocks");
    }
}

Q1996 medium

Which statement accurately describes a key difference between abstract classes and interfaces in Java (post-Java 8)?

Q1997 hard code output

Assume a file named 'empty.txt' exists but contains no characters (it's an empty file). What does this code print?

java

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

public class EmptyFileRead {
    public static void main(String[] args) throws IOException {
        // Assume 'empty.txt' is an empty file
        StringBuilder sb = new StringBuilder();
        int c = 0; // Initialize c outside the try-with-resources
        try (FileReader reader = new FileReader(new File("empty.txt"))) {
            while ((c = reader.read()) != -1) {
                sb.append((char) c);
            }
            if (sb.length() == 0) {
                sb.append("Empty");
            } else {
                sb.append("Not Empty");
            }
            sb.append(" - Read value after loop: " + c);
        }
        System.out.println(sb.toString());
    }
}

Q1998 medium code error

What is the compile-time or runtime error in the following Java code snippet when attempting to deserialize the object?

java

import java.io.*;

class DataHolder implements Externalizable {
    private int value1;
    private String value2;

    public DataHolder() {} // Required public no-arg constructor

    public DataHolder(int value1, String value2) {
        this.value1 = value1;
        this.value2 = value2;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeInt(value1); // Only writing value1
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        this.value1 = in.readInt();
        this.value2 = in.readUTF(); // Trying to read value2 which was not written
    }
}

public class SerializationQuestion7 {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        DataHolder data = new DataHolder(10, "Hello");
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("data.ser"))) {
            oos.writeObject(data);
        }

        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("data.ser"))) {
            DataHolder loadedData = (DataHolder) ois.readObject(); 
        }
    }
}

Q1999 medium

What is the primary guarantee provided by the `volatile` keyword in Java?

Q2000 hard

When using `Object.wait()` in Java for inter-thread communication, why is it crucial to always invoke `wait()` within a `while` loop instead of an `if` statement?

☕ Java MCQ Questions – Page 100