JavaConstructors
Java Constructors
A constructor in Java is aspecial method that is used to initialize objects.
The constructor is called when an object of a class is created.
It can be used to set initial values for object attributes:
Example
Create a constructor:
// Create a Main classpublic class Main { int x; // Create a class attribute // Create aclass constructor for the Main class public Main() { x = 5; // Set the initial value for the class attribute x } public static void main(String[] args) { Main myObj = new Main(); // Create an object of class Main (This willcall the constructor) System.out.println(myObj.x); // Print the value of x }}// Outputs 5Note that the constructor name mustmatch the class name, and it cannot have areturn type (likevoid).
Also note that the constructor is called when the object is created.
All classes have constructors by default: if you do not create a class constructor yourself, Java creates one for you. However, then you are not able to set initial values for object attributes.
Constructor Parameters
Constructors can also take parameters, which is used to initialize attributes.
The following example adds anint y parameter to the constructor. Inside the constructor we set x to y (x=y). When we call the constructor, we pass a parameter to the constructor (5), which will set the value of x to 5:
Example
public class Main { int x; public Main(int y) { x = y; } public static void main(String[] args) { Main myObj = new Main(5); System.out.println(myObj.x); }}// Outputs 5You can have as many parameters as you want:
Example
public class Main { int modelYear; String modelName; public Main(int year, String name) { modelYear = year; modelName = name; } public static void main(String[] args) { Main myCar = new Main(1969, "Mustang"); System.out.println(myCar.modelYear + " " + myCar.modelName); }}// Outputs 1969 Mustang
