public
, then it may be accessed by any Java code that can access the package in which it is declared. If a class or interface type is not declared public
, then it may be accessed only from within the package in which it is declared.public
, then access is permitted. All members of interfaces are implicitly public
.protected
, then access is permitted only when one of the following is true:
private
, then access is permitted only when it occurs from within the class in which it is declared.public
and Non-public
ClassesIf a class lacks the public
modifier, access to the class declaration is limited to the package in which it is declared (§6.6). In the example:
package points;
public class Point { public int x, y; public void move(int dx, int dy) { x += dx; y += dy; } }
class PointList { Point next, prev; }
two classes are declared in the compilation unit. The class Point
is available outside the package points
, while the class PointList
is available for access only within the package. Thus a compilation unit in another package can access points.Point
, either by using its fully qualified name:
package pointsUser;
class Test { public static void main(String[] args) { points.Point p = new points.Point(); System.out.println(p.x + " " + p.y); } }
or by using a single-type-import declaration (§7.5.1) that mentions the fully qualfied name, so that the simple name may be used thereafter:
package pointsUser;
import points.Point;
class Test { public static void main(String[] args) { Point p = new Point(); System.out.println(p.x + " " + p.y); } }
However, this compilation unit cannot use or import points.PointList
, which is not declared public
and is therefore inaccessible outside package points
.
If none of the access modifiers public
, protected
, or private
are specified, a class member or constructor is accessible throughout the package that contains the declaration of the class in which the class member is declared, but the class member or constructor is not accessible in any other package. If a public
class has a method or constructor with default access, then this method or constructor is not accessible to or inherited by a subclass declared outside this package.
package points;
public class Point { public int x, y; void move(int dx, int dy) { x += dx; y += dy; } public void moveAlso(int dx, int dy) { move(dx, dy); } }
then a subclass in another package may declare an unrelated move
method, with the same signature (§8.4.2) and return type. Because the original move
method is not accessible from package morepoints
, super
may not be used:
package morepoints;
public class PlusPoint extends points.Point { public void move(int dx, int dy) { super.move(dx, dy); // compile-time error moveAlso(dx, dy); } }
Because move of Point
is not overridden by move
in PlusPoint
, the method moveAlso
in Point
never calls the method move in PlusPoint
.
Thus if you delete the super.move
call from PlusPoint
and execute the test program:
import points.Point; import morepoints.PlusPoint; class Test { public static void main(String[] args) { PlusPoint pp = new PlusPoint(); pp.move(1, 1); }
}
it terminates normally. If move of Point
were overridden by move
in PlusPoint
, then this program would recurse infinitely, until a StackoverflowError
occurred.
private
Fields, Methods, and Constructors A
private
class member or constructor is accessible only within the class body in which the member is declared and is not inherited by subclasses. In the example:
class Point {
Point() { setMasterID(); }
int x, y; private int ID; private static int masterID = 0;
private void setMasterID() { ID = masterID++; }
}
the private
members ID,
masterID
, and setMasterID
may be used only within the body of class Point
. They may not be accessed by qualified names, field access expressions, or method invocation expressions outside the body of the declaration of Point
.