public

6.6.1 Determining Accessibility

6.6.4 Example: Access to public and Non-public Classes

If 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.

6.6.5 Example: Default-Access Fields, Methods, and Constructors

a name="36155"> 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.

For example, if we have:


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.

6.6.6 Example: public Fields, Methods, and Constructors

A public class member or constructor is accessible throughout the package where it is declared and from any other package that has access to the package in which it is declared. For example, in the compilation unit:


package points;

public class Point {


int x, y;
public void move(int dx, int dy) { x += dx; y += dy; moves++; }

public static int moves = 0;
}

the public class Point has as public members the move method and the moves field. These public members are accessible to any other package that has access to package points. The fields x and y are not public and therefore are accessible only from within the package points.