Constructors in Java | Type and Uses of Constructor

Constructors in Java

A constructor is a special method in Java that is used to initialize objects. It is called automatically when an object of a class is created. Constructors have the same name as the class and do not have a return type. They can be used to set initial values for object attributes or perform any other necessary initialization tasks.

Types of Constructors

Constructor Type	Description	Example
Default Constructor	Constructor with no parameters.	public MyClass() {}
Parameterized Constructor	Constructor with parameters.	public MyClass(int x, String y) {}
Copy Constructor	Constructor that creates an object by copying the values from another object of the same class.	public MyClass(MyClass obj) {}
Private Constructor	Constructor that is marked as private and used for preventing the instantiation of a class.	private MyClass() {}
Static Constructor	Constructor that is used to initialize static variables or perform other static initialization tasks.	static { /* static initialization code */ }

Examples

Here are five examples demonstrating the use of constructors in Java:

1. Default Constructor

   public class Person {
       private String name;
       
       public Person() {
           name = "Unknown";
       }
   }

2. Parameterized Constructor

   public class Car {
       private String brand;
       private int year;
       
       public Car(String brand, int year) {
           this.brand = brand;
           this.year = year;
       }
   }

3. Copy Constructor

   public class Point {
       private int x;
       private int y;
       
       public Point(Point other) {
           this.x = other.x;
           this.y = other.y;
       }
   }

4. Private Constructor

   public class Singleton {
       private static Singleton instance;
       
       private Singleton() {
           // Private constructor to prevent instantiation
       }
       
       public static Singleton getInstance() {
           if (instance == null) {
               instance = new Singleton();
           }
           return instance;
       }
   }

5. Static Constructor

   public class MathUtils {
       private static final double PI;
       
       static {
           PI = 3.14159;
       }
   }