Using Constructors : Constructor « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Constructor

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;
  }
}