I can imagine 3 type of visibility for variables (but I think there are more):
Variable is used within a method and any changes of the value of this variable are not visible from outside of the method (so it is local for a particular method).
A variable is local to the class meaning that it is unvisible from outisde of the class. However, any method of the class can easily see and change value of this variable without necessity to give the variable in the list of arguments of methods (so it is kind of global within the class).
Variable can be accessed by "objectName.variableName".
How do I declare these different kinds of variables?
1: just something like
int i;
within the method2: use the
private
modifier orprotected
modifier3: use
public
1) Any variable declared in a method is only visible in that method. (method-local). The programmer has no choice in that.
2) Any variable declared with the modifier
private
is visible only from within instances of the class it is delared in.3)
public
variables can be accessed from any class with object.variable;protected
variables can be accessed in this way from subclasses only;private
variables can be accesses in this way only within instances of the class the variable is declared in.For detail and reference, see the Java Learning Trail on Sun's website.
However: exposing class members (variables) to other classes is bad practise, and access should be enabled using methods, such as:
Important to remember: If you declare a variable in a class and don't use any access modifier it will be package-private. That means from other classes within the same package you can reference it with objectname.variable while from classes in other packages you can't.