Java Tutorials

• Constructor example

Constructors

• Constructors have the same name as the class they initialize.

    Body ()
    {
       idNum = nextID++;
    }
  

• Move the responsibility for idNum inside the Body class.

    Body sun = new Body();    // idNum is 0
    Body earth = new Body();  // idNum is 1
  

• Constructors can take zero or more parameters.
• Constructors have no return type.
• Constructors are invoked after the instance variables of the new object have been assigned their default initial values, and after their explicit initializers are executed.

Constructor example

• The following three classes demonstrate how constructors are called for classes and superclasses.

  public class ParentClass {
    public ParentClass() {
      System.out.println( "ParentClass constructor was called" );
    }
  }
  
  public class ChildClass extends ParentClass {
    public ChildClass() {
      System.out.println( "ChildClass constructor was called" );
    }
  }
  
  public class Main {
    public static void main(String[] args) {
      ChildClass cc = new ChildClass();
    }
  }