Java Constructors
Java Constructors
A constructor in Java is a special 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 MyClass class
public class MyClass {
int x; // Create a class attribute
// Create a class constructor for the MyClass class
public MyClass() {
x = 5; // Set the initial value for the class attribute x
}
public static void main(String[] args) {
MyClass myObj = new MyClass(); // Create an object of class MyClass (This will call the constructor)
System.out.println(myObj.x); // Print the value of x
}
}
// Outputs 5
Note that the constructor name must match the class name, and it cannot have a
return type (like void).
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 an int 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 MyClass {
int x;
public MyClass(int y) {
x = y;
}
public static void main(String[] args) {
MyClass myObj = new MyClass(5);
System.out.println(myObj.x);
}
}
// Outputs 5
You can have as many parameters as you want:
Example
public class Car {
int modelYear;
String modelName;
public Car(int year, String name) {
modelYear = year;
modelName = name;
}
public static void main(String[] args) {
Car myCar = new Car(1969, "Mustang");
System.out.println(myCar.modelYear + " " + myCar.modelName);
}
}
// Outputs 1969 Mustang
