One of the most widely used programming languages, Java, offers a variety of features as well as concepts that programmers need to comprehend. Java programming’s essential constructors and methods each have a specific purpose. In this article, we’ll look at the key differences between constructors and methods in Java, as well as how and when to utilize each in Java programming.

Key Differences Between Constructor and Method

Constructors and methods are vital concepts in Java programming, each of which has a specific function. It’s important for efficient coding to comprehend the differences between constructors and methods. So, below we have mentioned the key differences between Java constructors and methods.

What is Constructor in Java?

Method and Constructor in Java are different. Constructor is a block of codes that is similar to a method except for two things- its name is the same as the class name but it has no return type. It is used to create an instance of the class. But Sometimes constructor is also referred to as a special method to initialize an object. The constructor is executed at the time of creating an object of the class.

In object-oriented programming, both constructors and methods are used in classes to define behavior and functionality. However, there are some key differences between constructors and methods:

Rules for Java constructor

1. A constructor can’t be abstract, final, and static.
2. A constructor must be the same name as the class name.
3. Constructors have no return type.

Example:

public class Person {

    private String name;
    private int age;

    // Constructor
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Other methods and code for the Person class

    // Getter methods
    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    // Main method to test the Person class
    public static void main(String[] args) {
        // Creating a new Person object using the constructor
        Person person = new Person("Suresh", 20);

        // Accessing the object’s properties using getter methods
        System.out.println("Name: " + person.getName());
        System.out.println("Age: " + person.getAge());
    }
}
Code language: JavaScript (javascript)

In the above-mentioned example, the ‘Person’ class has a constructor that takes two parameters:’name’ and ‘age’. In the constructor, the values of this parameter are assigned to the corresponding instance variables by using the ‘this’ keyword.

In the ‘main’ method, we create a new ‘person’ object called ‘person’ using the constructor by providing names “Suresh” and “age 20”. we use the getter method to retrieve and display the values of the object’s properties.

What is Method in Java?

In Java, Method is a block of code that performs a specific task or action.It is a fundamental building block of Java programs and is used to encapsulate and again usable and modular code. these methods are defined within classes and can be called or invoked to execute their code.

A method typically consists of the following components:-

1. Method signature: This includes the method’s access modifier, return type, name, and parameter list. It defines the method and allows all other code to invoke it.

Example:

    Java code

public int calculateSum(int num1, int num2) {
    // Method code goes here
}
Code language: PHP (php)

In the above example, the method signature consists of the access modifier “public,” the return type “int,” the method name “calculateSum,” and the parameter list “(int num1, int num2).”

2.  Method Body: This is a block of code enclosed within braces’{}’. It contains the statements that define the function of the method. 

Example:

Java code

public int calculateSum(int num1, int num2) {
    int sum = num1 + num2; // Method body
    return sum;
}
Code language: PHP (php)

In the above code, the body of the method  calculates the sum of ‘num1’ and ‘num2’

and return the result of variable ’sum’.

3. Return Statement: A method may have a return statement, which specifies the value to be returned back to the code that invoked the method. The return type in the method signature should match the type of the value being returned. 

Example:

Java code

public int calculateSum(int num1, int num2) {
    int sum = num1 + num2;
    return sum; // Returning the sum
}
Code language: PHP (php)

In the above example, the method returns the calculated sum as an int value.

Methods can also be declared with a ‘void’ return type, which indicates that the method does not return any value. In such cases, the return statement can be omitted, or an empty ‘return’ statement can be used to exit the method without returning a value.

Methods are called or invoked using their name followed by parentheses, optionally passing the required arguments. The result of the method (if any) can be assigned to a variable or used directly in the code.

Example:

Java code

int result = calculateSum(6, 15);  // Invoking the method and storing the result
System.out.println(result);  // Printing the result
Code language: JavaScript (javascript)

in the above example, the ‘calculateSum’ method is invoked with arguments ‘6’ and’15’ and the return sum is stored in the ‘result’ variable, which is printed to the console.

Difference Between Constructor and Method in Java 

Below we have mentioned the key differences between Constructor and Method in Java based on various aspects including Purpose, Invocation, Return Type, Overloading, Inheritance, and Role in Object Initialization: 

1. Purpose

• Constructors: Constructors are special methods used to initialize objects of a class. They set initial values to instance variables and ensure the object is in a valid state upon creation.
• Methods: Methods are blocks of code that perform specific tasks, manipulate data, or return values. They encapsulate behavior and provide functionality to the program.

2. Invocation

• Constructors: Constructors are automatically invoked when an object is created using the new keyword. They are executed only once during object initialization.
• Methods: Methods are invoked by calling their names followed by parentheses, passing arguments if necessary. They can be called multiple times from different parts of the code.

3. Return Type

• Constructors: Constructors do not have an explicit return type. They implicitly return an instance of the class being constructed.
• Methods: Methods have explicit return types specified in their declarations. They can return values of various types or no value (void).

4. Overloading

• Constructors: Constructors can be overloaded by providing multiple constructors within a class, each with a different set of parameters. Overloaded constructors allow objects to be instantiated with different initial values.
• Methods: Methods can also be overloaded by defining multiple methods within a class with the same name but different parameters. Overloaded methods enable the execution of different operations based on the input arguments.

5. Inheritance

• Constructors: Constructors are not inherited in Java. However, the subclass constructor implicitly calls the superclass constructor using the super() keyword.
• Methods: Methods can be inherited from a superclass to a subclass. Subclasses can override inherited methods to provide their own implementation.

6. Role in Object Initialization

• Constructors: Constructors play a crucial role in object initialization. They initialize the state of an object by setting values to instance variables, allocating memory, and performing other initialization tasks.
• Methods: Methods perform specific operations or computations on objects, manipulate data, or provide functionality to the program.

Conclusion

In Java, constructors and methods serve distinct purposes and have specific characteristics. Constructors initialize objects, ensuring they are in a valid state upon creation, while methods perform operations, manipulate data, and provide functionality. Understanding the key differences between constructors and methods allows developers to utilize these elements effectively in their code. By leveraging constructors and methods appropriately, developers can build robust and efficient Java programs.