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
.
141






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