6.6.7

Example:

protected

 Fields, Methods, and Constructors

NAMES

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

.

6.6.7   Example:

protected

 Fields, Methods, and Constructors

Consider this example, where the

point

 package declares:

package points;

public class Point {

protected int x, y;

void warp(threePoint.Point3d a) {

if (a.z > 0)

//

compile time error: cannot access

a.z

a.delta(this);

}

}

and the

threePoint

 package declares:

package threePoint;

import points.Point;

public class Point3d extends Point {

protected int z;

public void delta(Point p) {

p.x += this.x;

//

compile time error: cannot access

p.x

p.y += this.y;

//

compile time error: cannot access

p.y

}

public void delta3d(Point3d q) {

q.x += this.x;

q.y += this.y;

q.z += this.z;

}

}

which defines a class

Point3d

. A compile time error occurs in the method

delta

here: it cannot access the protected members

x

 and

y

 of its parameter

p

, because

while

Point3d

 (the class in which the references to fields

x

 and

y

 occur) is a sub 

class of

Point

 (the class in which

x

 and

y

 are declared), it is not involved in the

implementation of a

Point

 (the type of the parameter

p

). The method

delta3d

can access the protected members of its parameter

q

, because the class

Point3d

 is

a subclass of

Point

 and is involved in the implementation of a

Point3d

.

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