ganeshkavhar / java-constructor

ganesh kavhar java tutorials

Java-constructor

ganesh kavhar java tutorials

A constructor initializes an object when it is created. It has the same name as its class and is syntactically similar to a method. However, constructors have no explicit return type.

Typically, you will use a constructor to give initial values to the instance variables defined by the class, or to perform any other start-up procedures required to create a fully formed object.

All classes have constructors, whether you define one or not, because Java automatically provides a default constructor that initializes all member variables to zero. However, once you define your own constructor, the default constructor is no longer used.

Syntax Following is the syntax of a constructor −

class ClassName { ClassName() { } } Java allows two types of constructors namely −

No argument Constructors Parameterized Constructors No argument Constructors As the name specifies the no argument constructors of Java does not accept any parameters instead, using these constructors the instance variables of a method will be initialized with fixed values for all objects.

Example Public class MyClass { Int num; MyClass() { num = 100; } } You would call constructor to initialize objects as follows

public class ConsDemo { public static void main(String args[]) { MyClass t1 = new MyClass(); MyClass t2 = new MyClass(); System.out.println(t1.num + " " + t2.num); } } This would produce the following result

100 100 Parameterized Constructors Most often, you will need a constructor that accepts one or more parameters. Parameters are added to a constructor in the same way that they are added to a method, just declare them inside the parentheses after the constructor's name.

Example Here is a simple example that uses a constructor −

// A simple constructor. class MyClass { int x;

// Following is the constructor MyClass(int i ) { x = i; } } You would call constructor to initialize objects as follows −

public class ConsDemo { public static void main(String args[]) { MyClass t1 = new MyClass( 10 ); MyClass t2 = new MyClass( 20 ); System.out.println(t1.x + " " + t2.x); } } This would produce the following result −

10 20