Java Interview Questions: Final vs. Finally Keywords

Keywords in Java

• Final and finally are predefined keywords in Java.
• Many predefined keywords in Java.

Final Keyword

• Can be used with variables, methods, and classes.
• Final Variables: Once initialized, cannot be updated (become constants).
• Final Methods: Cannot be overridden by child classes.
• Final Classes: Cannot be inherited by other classes (e.g., no child classes).
• Practical demonstration in Eclipse ID: Used final with variables, methods, and classes.

Finally Keyword

• Used in exception handling.
• Finally block always executes regardless of try/catch block execution.
• Typically used to close objects or clean up resources.
• Example: Closing scanner objects or file streams.

Java Interview Questions: Accessing Private Methods

Private Methods and Variables

• Private variables and methods cannot be accessed directly outside the class.
• Encapsulation can be used to indirectly access private members through public methods.

Encapsulation Example

• Create a public method within the same class as the private member.
• Call the private method or variable within this public method.
• Access the public method from outside the class.

Java Interview Questions: Converting Array to ArrayList & ArrayList to Array

Converting Array to ArrayList

1. Convert the array to a list using Arrays.asList().
2. Pass the list to the ArrayList constructor.

Integer[] array = {1, 2, 3, 4};
List<Integer> list = Arrays.asList(array);
ArrayList<Integer> arrayList = new ArrayList<>(list);

Converting ArrayList to Array

1. Create an array with the same size as the ArrayList.
2. Use toArray() method of ArrayList.

ArrayList<Integer> arrayList = new ArrayList<>();
arrayList.add(1);
arrayList.add(2);
Integer[] array = new Integer[arrayList.size()];
array = arrayList.toArray(array);

Java Interview Questions: Static Keyword Usage

Purpose of Static Keyword

• Static variables and methods can be accessed without creating an object of the class.
• Accessed using the class name directly.
• Example: With and without static keyword for variables and methods.

class Car {
    static String color;
    static void startCar() {
        System.out.println("Car started");
    }
}

// Accessed directly without creating an object
Car.color = "Black";
Car.startCar();

Java Interview Questions: Synchronized Block in Java

Purpose of Synchronized Block

• Used for thread safety in multi-threaded environments.
• Ensures that only one thread can access a particular resource at a time.
• Example: Bank account balance update with synchronized block.

class BankAccount {
    private int balance = 0;
    public void deposit(int amount) {
        synchronized(this) {
            balance += amount;
        }
    }
    public int getBalance() {
        return balance;
    }
}