Java Methods
Java Methods Interview with follow-up questions
Interview Question Index
- Question 1: What is a method in Java and why is it used?
- Follow up 1 : Can you explain the structure of a method?
- Follow up 2 : What is the difference between a method and a function?
- Follow up 3 : What are the different types of methods in Java?
- Follow up 4 : Can you provide an example of a method?
- Question 2: What are the rules for defining a method in Java?
- Follow up 1 : What happens if we don't follow these rules?
- Follow up 2 : Can you provide an example of a correctly defined method?
- Follow up 3 : What is the role of the return type in a method?
- Follow up 4 : Can a method have the same name as its class?
- Question 3: What is method overloading in Java?
- Follow up 1 : Can you provide an example of method overloading?
- Follow up 2 : What are the rules for method overloading?
- Follow up 3 : What is the advantage of method overloading?
- Follow up 4 : Is it possible to overload main() method in Java?
- Question 4: What is method overriding in Java?
- Follow up 1 : Can you provide an example of method overriding?
- Follow up 2 : What are the rules for method overriding?
- Follow up 3 : What is the advantage of method overriding?
- Follow up 4 : Can we override static method in Java?
- Question 5: What is the difference between method overloading and method overriding?
- Follow up 1 : Can you provide an example to illustrate the difference?
- Follow up 2 : In what scenarios would you use method overloading versus method overriding?
- Follow up 3 : What is the impact on performance for each?
- Follow up 4 : Can both be used in the same class?
Question 1: What is a method in Java and why is it used?
Answer:
In Java, a method is a collection of statements that are grouped together to perform a specific task. It is used to break down a complex program into smaller, more manageable pieces. Methods provide code reusability, improve readability, and allow for modular programming.
Follow up 1: Can you explain the structure of a method?
Answer:
A method in Java has the following structure:
() {
// method body
// statements
// return statement (if applicable)
}
- The
access_modifier
determines the visibility of the method (e.g.,public
,private
,protected
). - The
return_type
specifies the type of value that the method returns. If the method does not return a value, the return type isvoid
. - The
method_name
is the identifier for the method. - The
parameter_list
specifies the input parameters that the method accepts. - The method body contains the statements that define the functionality of the method.
- The return statement is used to return a value from the method (if applicable).
Follow up 2: What is the difference between a method and a function?
Answer:
In Java, the terms 'method' and 'function' are often used interchangeably, but there is a subtle difference between them. A method is a piece of code that is associated with an object or a class, whereas a function is a standalone piece of code that can be called independently.
In other words, a method is always associated with an object or a class, and it can access the instance variables and methods of that object or class. On the other hand, a function is not associated with any object or class, and it can only access the variables and methods that are passed to it as arguments.
Follow up 3: What are the different types of methods in Java?
Answer:
There are several types of methods in Java:
- Instance methods: These methods are associated with an instance of a class and can access the instance variables and methods.
- Static methods: These methods belong to the class itself and can be called without creating an instance of the class.
- Constructor methods: These methods are used to create and initialize objects of a class.
- Getter and setter methods: These methods are used to get and set the values of the instance variables.
- Overloaded methods: These methods have the same name but different parameter lists.
- Recursive methods: These methods call themselves to solve a problem by breaking it down into smaller subproblems.
- Abstract methods: These methods are declared in an abstract class or interface and do not have a body. They are implemented by the subclasses or implementing classes.
Follow up 4: Can you provide an example of a method?
Answer:
Sure! Here's an example of a method in Java:
public class Calculator {
public int add(int num1, int num2) {
int sum = num1 + num2;
return sum;
}
}
In this example, the Calculator
class has a method called add
that takes two integers as input parameters and returns their sum. The method is declared as public
, so it can be accessed from other classes. Inside the method, the sum of the two numbers is calculated and stored in a variable called sum
. Finally, the sum
variable is returned as the result of the method.
Question 2: What are the rules for defining a method in Java?
Answer:
The rules for defining a method in Java are as follows:
- The method must have a unique name within its class.
- The method must have a return type, which specifies the type of value that the method will return. If the method does not return a value, the return type should be
void
. - The method can have zero or more parameters, which are values that are passed into the method for it to use.
- The method can have an access modifier, such as
public
orprivate
, which determines whether the method can be accessed from other classes. - The method can have a list of exceptions that it throws, which specifies the types of exceptions that can occur during the execution of the method.
Follow up 1: What happens if we don't follow these rules?
Answer:
If we don't follow the rules for defining a method in Java, the code will not compile and we will get a compilation error. The compiler will check for any violations of the method definition rules and report them as errors.
Follow up 2: Can you provide an example of a correctly defined method?
Answer:
Sure! Here's an example of a correctly defined method in Java:
public int addNumbers(int a, int b) {
int sum = a + b;
return sum;
}
In this example, the method is named addNumbers
and it takes two parameters of type int
. It calculates the sum of the two numbers and returns the result as an int
value.
Follow up 3: What is the role of the return type in a method?
Answer:
The return type in a method specifies the type of value that the method will return. It indicates the type of data that the method will produce as its result. The return type is declared before the method name in the method signature. If the method does not return a value, the return type should be void
.
Follow up 4: Can a method have the same name as its class?
Answer:
Yes, a method can have the same name as its class. This type of method is called a constructor. A constructor is a special method that is used to initialize objects of a class. It has the same name as the class and does not have a return type. Constructors are called automatically when an object is created using the new
keyword.
Question 3: What is method overloading in Java?
Answer:
Method overloading in Java is the ability to define multiple methods with the same name but with different parameters. It allows a class to have multiple methods with the same name but different arguments. The compiler determines which method to call based on the number of arguments and their types.
Follow up 1: Can you provide an example of method overloading?
Answer:
Sure! Here's an example of method overloading in Java:
public class Calculator {
public int add(int a, int b) {
return a + b;
}
public double add(double a, double b) {
return a + b;
}
}
Calculator calculator = new Calculator();
int result1 = calculator.add(5, 10); // Calls the first add method
double result2 = calculator.add(3.5, 2.5); // Calls the second add method
Follow up 2: What are the rules for method overloading?
Answer:
The rules for method overloading in Java are as follows:
- The methods must have the same name.
- The methods must have different parameter lists (number of parameters or types of parameters).
- The methods may have different return types, but it is not considered for method overloading.
- The methods may have different access modifiers.
- The methods may throw different exceptions.
Follow up 3: What is the advantage of method overloading?
Answer:
The advantages of method overloading in Java are:
- Readability: Method overloading allows developers to use the same method name for similar operations, making the code more readable and easier to understand.
- Reusability: Method overloading promotes code reusability by allowing multiple methods with the same name to perform different tasks based on the parameters.
- Flexibility: Method overloading provides flexibility in choosing the appropriate method based on the arguments passed.
Follow up 4: Is it possible to overload main() method in Java?
Answer:
Yes, it is possible to overload the main() method in Java. The main() method can be overloaded by defining multiple methods with the same name but different parameter lists. However, only the main() method with the standard signature (public static void main(String[] args)) will be executed when the program is run from the command line.
Question 4: What is method overriding in Java?
Answer:
Method overriding is a feature in Java where a subclass provides its own implementation of a method that is already defined in its superclass. The method in the subclass must have the same name, return type, and parameters as the method in the superclass. By overriding a method, the subclass can modify or extend the behavior of the superclass method.
Follow up 1: Can you provide an example of method overriding?
Answer:
Sure! Here's an example:
class Animal {
public void makeSound() {
System.out.println("Animal is making a sound");
}
}
class Dog extends Animal {
@Override
public void makeSound() {
System.out.println("Dog is barking");
}
}
public class Main {
public static void main(String[] args) {
Animal animal = new Animal();
animal.makeSound(); // Output: Animal is making a sound
Dog dog = new Dog();
dog.makeSound(); // Output: Dog is barking
}
}
In this example, the Dog
class extends the Animal
class and overrides the makeSound()
method. When the makeSound()
method is called on an instance of Dog
, it prints "Dog is barking" instead of the default message from the Animal
class.
Follow up 2: What are the rules for method overriding?
Answer:
The rules for method overriding in Java are as follows:
- The method in the subclass must have the same name, return type, and parameters as the method in the superclass.
- The access level of the overriding method cannot be more restrictive than the access level of the method being overridden. For example, if the method in the superclass is declared as
public
, the overriding method in the subclass must also be declared aspublic
. - The overriding method cannot throw a checked exception that is not declared by the overridden method. However, it can throw a narrower or unchecked exception.
- The
@Override
annotation should be used to indicate that a method is intended to override a superclass method. This is optional but recommended for better code readability and to catch any accidental mistakes in method signature.
Follow up 3: What is the advantage of method overriding?
Answer:
The advantage of method overriding is that it allows a subclass to provide its own implementation of a method defined in its superclass. This enables the subclass to modify or extend the behavior of the superclass method according to its specific requirements. Method overriding is a key feature of polymorphism in object-oriented programming, as it allows different objects to respond to the same method call in different ways.
Follow up 4: Can we override static method in Java?
Answer:
No, we cannot override static methods in Java. When a method is declared as static, it belongs to the class rather than an instance of the class. Subclasses cannot override static methods because they are associated with the class itself, not with individual objects. However, it is possible to declare a static method with the same name in the subclass, but it will not be considered as an overriding method. Instead, it will be treated as a separate method that hides the static method of the superclass.
Question 5: What is the difference between method overloading and method overriding?
Answer:
Method overloading and method overriding are both concepts in object-oriented programming that involve the use of methods in classes.
Method overloading refers to the ability to define multiple methods with the same name but different parameters in a class. These methods can have different return types, different number of parameters, or different types of parameters. The compiler determines which method to call based on the arguments passed to it.
Method overriding, on the other hand, occurs when a subclass provides a specific implementation of a method that is already defined in its superclass. The method in the subclass must have the same name, return type, and parameters as the method in the superclass.
In summary, method overloading is about having multiple methods with the same name but different parameters in the same class, while method overriding is about providing a specific implementation of a method in a subclass that is already defined in its superclass.
Follow up 1: Can you provide an example to illustrate the difference?
Answer:
Sure! Here's an example to illustrate the difference between method overloading and method overriding:
public class Shape {
public void draw() {
System.out.println("Drawing a shape");
}
}
public class Circle extends Shape {
public void draw() {
System.out.println("Drawing a circle");
}
public void draw(int radius) {
System.out.println("Drawing a circle with radius " + radius);
}
}
public class Main {
public static void main(String[] args) {
Shape shape = new Shape();
shape.draw(); // Output: "Drawing a shape"
Circle circle = new Circle();
circle.draw(); // Output: "Drawing a circle"
circle.draw(5); // Output: "Drawing a circle with radius 5"
}
}
In this example, the Shape
class has a draw
method that prints "Drawing a shape". The Circle
class extends the Shape
class and overrides the draw
method to print "Drawing a circle". It also overloads the draw
method by adding a new method with an additional int
parameter to print "Drawing a circle with radius [radius]".
When the draw
method is called on an instance of the Shape
class, it calls the draw
method in the Shape
class. When the draw
method is called on an instance of the Circle
class, it calls the overridden draw
method in the Circle
class. When the draw
method with an int
parameter is called on an instance of the Circle
class, it calls the overloaded draw
method in the Circle
class.
Follow up 2: In what scenarios would you use method overloading versus method overriding?
Answer:
Method overloading is useful when you want to provide multiple ways to perform a similar operation with different parameters. For example, you might have a calculateArea
method that can calculate the area of a square, rectangle, or circle by accepting different parameters. Method overloading allows you to define multiple calculateArea
methods with different parameter types or numbers.
Method overriding, on the other hand, is useful when you want to provide a specific implementation of a method in a subclass that is different from the implementation in the superclass. This is often used when you want to customize the behavior of a method for a specific subclass.
In summary, method overloading is used when you want to provide multiple ways to perform a similar operation, while method overriding is used when you want to provide a specific implementation of a method in a subclass.
Follow up 3: What is the impact on performance for each?
Answer:
In terms of performance, method overloading and method overriding have different impacts.
Method overloading has no significant impact on performance because the decision of which method to call is made at compile-time based on the arguments passed to it. The compiler determines the appropriate method to call based on the method signature.
Method overriding, on the other hand, can have a slight impact on performance because the decision of which method to call is made at runtime. When a method is overridden, the JVM needs to determine the actual type of the object at runtime and then call the appropriate method based on the actual type.
However, the impact on performance is usually negligible unless there are a large number of method calls or the method being overridden is computationally intensive.
In general, it is more important to focus on code readability, maintainability, and design principles when deciding whether to use method overloading or method overriding, rather than solely considering performance.
Follow up 4: Can both be used in the same class?
Answer:
Yes, both method overloading and method overriding can be used in the same class.
Method overloading allows you to define multiple methods with the same name but different parameters in a class. These methods can have different return types, different number of parameters, or different types of parameters.
Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its superclass. The method in the subclass must have the same name, return type, and parameters as the method in the superclass.
By using both method overloading and method overriding, you can provide multiple ways to perform a similar operation with different parameters and also customize the behavior of a method for a specific subclass.
It is important to note that method overloading and method overriding are independent concepts and serve different purposes, so they can be used together in the same class without any issues.