The Java Language Specification, Third Edition

8.4.10 Examples of Method Declarations CLASSES
232
class RealPoint extends Point {
float x = 0.0f, y = 0.0f;
void move(int dx, int dy) { move((float)dx, (float)dy); }
void move(float dx, float dy) { x += dx; y += dy; }
float getX() { return x; }
float getY() { return y; }
}
Here the class Point provides methods getX and getY that return the values of its
fields x and y; the class RealPoint then overrides these methods by declaring
methods with the same signature. The result is two errors at compile time, one for
each method, because the return types do not match; the methods in class Point
return values of type int, but the wanna-be overriding methods in class
RealPoint return values of type float.
8.4.10.4 Example: Overriding versus Hiding
This example corrects the errors of the example in the preceding section:
class Point {
int x = 0, y = 0;
void move(int dx, int dy) { x += dx; y += dy; }
int getX() { return x; }
int getY() { return y; }
int color;
}
class RealPoint extends Point {
DRAFT
float x = 0.0f, y = 0.0f;
void move(int dx, int dy) { move((float)dx, (float)dy); }
void move(float dx, float dy) { x += dx; y += dy; }
int getX() { return (int)Math.floor(x); }
int getY() { return (int)Math.floor(y); }
}
Here the overriding methods getX and getY in class RealPoint have the same
return types as the methods of class Point that they override, so this code can be
successfully compiled.