Java Objects

Objects are containers around aggregates of primitive types, arrays, and other objects

• Properties of Classes

• All Java code is contained within objects
  Excepted comments, import and package statements.

• Objects are passed to methods by reference

• Definition, declaration, and creation of objects are distinct

• Instances of objects are created with new and have a value of null

• Objects have four forms: the class, the abstract class, the inner class, and the interface

class Circle						// object definition
{	static double pi = 3.141592;	// class variable
	double radius;					// instance variable
	public Circle(double r)			// constructor method
	{	radius = r;
	}
	public double circumference()	{	return 2*pi*radius; }
	public double area()	{	return pi*radius*radius; }
	public static getPi()	{	return pi;	}	// class method
}
   
Circle c;				// object declaration
c = new Circle(4.0);	// object creation
double a = c.area();	// object method call