essay25.txt

Java Essay Serials 1 - Java Basics - 25, Static variable vs Instance variable
A static variable is belong to a class, while an instance variable is belong to an instance. Hence a static variable can be shared among all instances.

For example, we define a static variable in AClass:
class AClass {
    public static int num = 10;
}
The static variable num can be accessed without an instance:
class Test {
    public void read() {
        int n = AClass.num;
    }
}

And we can also access the static variable in an instance, for example:
	public void write() {
		AClass a = new AClass();
		a.num = 20;
	}
Here we create a new instance of AClass, then access the static variable via the instance.
It works but not recommended. Actually the compiler would complain a warning "The static field AClass.num should be accessed in a static way".
It's practically not good to access static variable via instance, Josh Bloch said that's a "bad decision".

From Java 8 onwards, the static variables and constants are stored in the Heap, in the Class object associated with instances.