Static and non static fields

Question

just to clarify I am thinking of this right, in java a static field is a variable/field which is used by a whole class, or can be used by all objects refering to that class?

Answer 1

An instance attribute is one that is specific to an instance, and its value isn't shared among other instances of the same class.

On the other hand, a class (or static) attribute is one that is common to all of the class' instances, as it belongs to the class, not to an instance in particular.

So you must be careful with the static attributes, because a change in one will be reflected on all of the code that uses it, sometimes causing unexpected results. In practice, I tend to avoid static attributes, except for the cases where they have constant, immutable values.

Similar considerations apply to instance methods and static methods: an instance method can "see" both instance and static methods and attributes, whereas a static method can only refer to static methods and attributes of the class, and can't "see" the instance methods and attributes (that is unless it instantiates an object and uses it to access its instance members).