How to control visibility of variables in Java?

Question

I can imagine 3 type of visibility for variables (but I think there are more):

1. Variable is used within a method and any changes of the value of this variable ar

Answer 1

1: just something like int i; within the method

2: use the private modifier or protected modifier

3: use public

Answer 2

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.

Answer 3

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:

public class MyClass {
  private int myInt;

  public int getMyInt() {
    return myInt;
  }

  public void setMyInt(int newInt) {
    myInt = newInt;
  }
}