variable declaration

The association of a variable with a particular type. It is important to make a distinction between the declaration of variables of primitive types and those of class types. A variable of primitive type acts as a container for a single value of its declared type. Declaration of a variable of a class type does not automatically cause an object of that type to be constructed and, by default, the variable will contain the value null. A variable of a class type acts as a holder for a reference to an object that is compatible with the variable's class type. Java's rules of polymorphism allow a variable of a class type to hold a reference to any object of its declared type or any of its sub types. A variable with a declared type of Object, therefore, may hold a reference to an object of any class, therefore.