CLASSES

Examples of Inheritance

8.2.1

public class Point {

public int x, y;

protected int useCount = 0;

static protected int totalUseCount = 0;

public void move(int dx, int dy) {

x += dx; y += dy; useCount++; totalUseCount++;

}

}

the

public

 and

protected

 fields

x

,

y

,

useCount

 and

totalUseCount

 are inher 

ited in all subclasses of

Point

. Therefore, this test program, in another package,

can be compiled successfully:

class Test extends points.Point {

public void moveBack(int dx, int dy) {

x  = dx; y  = dy; useCount++; totalUseCount++;

}

}

8.2.1.3

Inheritance with

private

In the example:

class Point {

int x, y;

void move(int dx, int dy) {

x += dx; y += dy; totalMoves++;

}

private static int totalMoves;

void printMoves() { System.out.println(totalMoves); }

}

class Point3d extends Point {

int z;

void move(int dx, int dy, int dz) {

super.move(dx, dy); z += dz; totalMoves++;

}

}

the class variable

totalMoves

 can be used only within the class

Point

; it is not

inherited by the subclass

Point3d

. A compile time error occurs at the point where

method

move

 of class

Point3d

 tries to increment

totalMoves

.

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