CLASSES

Examples of Method Declarations

8.4.8

(0, 0)

(2.7182798, 3.14159)

(2, 3)

(2, 3)

The first line of output illustrates the fact that an instance of

RealPoint

 actu 

ally contains the two integer fields declared in class

Point

; it is just that their

names are hidden from code that occurs within the declaration of class

RealPoint

 (and those of any subclasses it might have). When a reference to an

instance of class

RealPoint

 in a variable of type

Point

 is used to access the field

x

, the integer field

x

 declared in class

Point

 is accessed. The fact that its value is

zero indicates that the method invocation

p.move(1,  1)

 did not invoke the

method

move

 of class

Point

; instead, it invoked the overriding method

move

 of

class

RealPoint

.

The second line of output shows that the field access

rp.x

 refers to the field

x

declared in class

RealPoint

. This field is of type

float

, and this second line of

output accordingly displays floating point values. Incidentally, this also illustrates

the fact that the method name

show

 is overloaded; the types of the arguments in

the method invocation dictate which of the two definitions will be invoked.

The last two lines of output show that the method invocations

p.getX()

 and

rp.getX()

 each invoke the

getX

 method declared in class

RealPoint

. Indeed,

there is no way to invoke the

getX

 method of class

Point

 for an instance of class

RealPoint

 from outside the body of

RealPoint

, no matter what the type of the

variable we may use to hold the reference to the object. Thus, we see that fields

and methods behave differently: hiding is different from overriding.

8.4.8.5

Example: Invocation of Hidden Class Methods

A hidden class (

static

) method can be invoked by using a reference whose type

is the class that actually contains the declaration of the method. In this respect,

hiding of static methods is different from overriding of instance methods. The

example:

class Super {

static String greeting() { return "Goodnight"; }

String name() { return "Richard"; }

}

class Sub extends Super {

static String greeting() { return "Hello"; }

String name() { return "Dick"; }

}

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