And if no class instance is created, the non-static variable is never initialized and there is no value to reference. Consequently, attempting to access a non-static variable from a static context (a static method or block) without a class instance creates ambiguity-every instantiated object has its own variable, so the compiler is unable to tell which value is being referenced. On the other hand, a non-static variable is initialized every time a new instance of its class is created, and as such there can be multiple copies of it in memory, each with a different value.
Non-static Variable X Cannot be Referenced from a Static Context & Non-static Method X Cannot be Referenced from a Static ContextĪ static variable is initialized once, when its class is loaded into memory, and its value is shared among all instances of that class. This is because instance variables and methods are always tied to a specific instance, i.e., object of their class.ĭue to their instance-less nature, static variables and methods are sometimes used to construct stateless utility classes. Namely, static methods can only use static variables and call static methods-they cannot access instance variables or methods directly, without an object reference. However, not all combinations of instance and class variables and methods are allowed. Ī common use for static methods is to access static variables. Class variables and methods are stored in fixed locations in memory and are accessed without a reference to an object, directly through the class name itself. Hence, static variables are often called class variables, while static methods are commonly referred to as class methods. In other words, the static modifier is used to define variables and methods related to the class as a whole, rather than to an instance (object) of the class.
The static keyword in Java is a modifier that makes a member of a class independent of the instances of that class. Introduction to Static Variables and Methods
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