CLASSES

Examples of Method Declarations

8.4.8

the class

RealPoint

 hides the declarations of the

int

 instance variables

x

 and

y

of class

Point

 with its own

float

 instance variables

x

 and

y

, and overrides the

method

move

 of class

Point

 with its own

move

 method. It also overloads the name

move

 with another method with a different signature ( 8.4.2).

In this example, the members of the class

RealPoint

 include the instance

variable

color

 inherited from the class

Point

, the

float

 instance variables

x

 and

y

 declared in

RealPoint

, and the two

move

 methods declared in

RealPoint

.

Which of these overloaded

move

 methods of class

RealPoint

 will be chosen

for any particular method invocation will be determined at compile time by the

overloading resolution procedure described in  15.11.

8.4.8.3

Example: Incorrect Overriding

This example is an extended variation of that in the preceding section:

class Point {

int x = 0, y = 0, color;

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

int getX() { return x; }

int getY() { return y; }

}

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

.

8.4.8.4

Example: Overriding versus Hiding

This example corrects the errors of the example in the preceding section:

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