• All non-static members (variables , methods) are called instance members.

• Instance members are encapsulated into object.

• Every object has its own copy of instance members.

• Instance data fields (either variable or constants)
• Instance methods
• Non-static initializer block (instance block)
• Inner class

Non-static/Instance Variable :

• Instance variables are declared in a class, but outside a method.

• When a space is allocated for an object in the heap, a slot for each instance variable value is created.

• Instance variables have default values. For numbers the default value is 0, for Booleans it is false and for object references it is null.

Example

class Demo
{
 int x;
 public static void main(String []arg)
 {
  Demo ob1 = new Demo();
  Demo ob2 = new Demo();
 }
}

 Here x is non-static variable of integer type in class Demo.
 There will be separate copy of x created for all instance of Demo class.
            

Non-static Method

• Usually create to operate instance data of the class.

• A non-static method can access other static & non-static members (variables, methods) in the same class directly.

• A non-static method implicitly provides 2 references :

  • this : Reference to the current object.

  • super : Reference to the super object.

Example

class Demo
{
 int x;
 static int y ;
 void show()
 {
/* direct accessing of both static
   and non-static */
  System.out.println("x :"+x);
  System.out.println("y :"+y);
 }
 public static void main(String []arg)
 {
  Demo ob1 = new Demo();
/*since show is non-static object is
required to access in static method */
      ob1.show();
 }
}
            

Non-Static Block :

• Non-static block of code provided in the class, execute every time an object of the class is constructed.

• It automatically executes right after the allocation of non-static data fields and just before the invocation of constructor.

• It can be used to initialized the non-static data fields with some dynamic value.

Example

class Demo
{
 // non-static block
 {
System.out.println("Non-Static Block");
 }
 public static void main(String []arg)
 {
  Demo ob1 = new Demo();
  Demo ob2 = new Demo();
  //Anonumous Object
  new Demo();
 }
}           

Non-Static Block
Non-Static Block
Non-Static Block