Using Constructors : Constructor « Class Definition « Java Tutorial

  1. Every class must have at least one constructor.
  2. If there is no constructors for your class, the compiler will supply a default constructor(no-arg constructor).
  3. A constructor is used to construct an object.
  4. A constructor looks like a method and is sometimes called a constructor method.
  5. A constructor never returns a value
  6. A constructor always has the same name as the class.
  7. A constructor may have zero argument, in which case it is called a no-argument (or no-arg, for short) constructor.
  8. Constructor arguments can be used to initialize the fields in the object.

The syntax for a constructor is as follows.

constructorName (listOfArguments) {
    [constructor body]
public class MainClass {
  double radius;

  // Class constructor
  MainClass(double theRadius) {
    radius = theRadius;

5.2.1.Using Constructors
5.2.2.The Default Constructor
5.2.3.Multiple Constructors
5.2.4.Calling a Constructor From a Constructor
5.2.5.Duplicating Objects using a Constructor
5.2.6.Class Initializer: during declaration
5.2.7.Order of constructor calls