6.6.3 An Example of Access Control

For examples of access control, consider the two compilation units:

package points;

class PointVec { Point[] vec; }

and:

package points;

public class Point {
	protected int x, y;
	public void move(int dx, int dy) { x += dx; y += dy; }
	public int getX() { return x; }
	public int getY() { return y; }
}

which declare two class types in the package points:

• The class type PointVec is not public and not part of the public interface of the package points, but rather can be used only by other classes in the package.
• The class type Point is declared public and is available to other packages. It is part of the public interface of the package points.
• The methods move, getX, and getY of the class Point are declared public and so are available to any Java code that uses an object of type Point.
• The fields x and y are declared protected and are accessible outside the package points only in subclasses of class Point, and only when they are fields of objects that are being implemented by the code that is accessing them.

See §6.6.7 for an example of how the protected access modifier limits access.