Instance,static and local variables in JAVA

Variables are classified based on storage and place where we are declared.

Based on storage:

v  Reference variables: Used to holds object references

              Ex: String s = “raju”; // s is reference variable

                       SampleDemo  sd = new SampleDemo(); // sd is reference variable

v  Primitive variable: Used to holds primitive values

                                                   Ex: int i=10;

                                                   char c=‘s’; 

Based on place where we declared:

             v  Instance variables

             v  Static variables

             v  Local variables

        

            Instance variables:

v   Instance variables are object level variables

v  For each object one separate instance variable will creates

v  Each instance variables will get default values which is depends on the variable declared type

v  These variables are activated wherever object creates and gets deactivated whenever the object destroyed by the Garbage Collector

v  All instance variables will store in Heap memory

v  We should declare the variables outside the methods of a class

v  Object is used for accessing the instance variables

              Static variables:

v  A single copy of the static variable will be shared by all the instances of same class

v  A static variable will be creates at the time of class loading time into memory and it destroyed at the time of class unloaded from the memory

v  Static variable will gets default values

v  Static will have “static” modifier

              Ex: static int i;

v  Static variables should define outside of all the methods of a class

               Ex: Student s1 = new Student();

                      Student s2 = new Student();

v  Class name is enough for accessing the static variables

                 Local variable:

v  The variables which are declared in a method or as a method arguments or in a constructor or in block are called local variables

v  Local variable will not get default values

v  Before using the local variables must initialized

v  Otherwise we will gets compilation error