CLASSES

Examples of Field Declarations

8.3.3

8.3.3.1

Example: Hiding of Class Variables

The example:

class Point {

static int x = 2;

}

class Test extends Point {

static double x = 4.7;

public static void main(String[] args) {

new Test().printX();

}

void printX() {

System.out.println(x + " " + super.x);

}

}

produces the output:

4.7 2

because the declaration of

x

 in class

Test

 hides the definition of

x

 in class

Point

,

so class

Test

 does not inherit the field

x

 from its superclass

Point

. Within the

declaration of class

Test

, the simple name

x

 refers to the field declared within

class

Test

. Code in class

Test

 may refer to the field

x

 of class

Point

 as

super.x

(or, because

x

 is

static

, as

Point.x

). If the declaration of

Test.x

 is deleted:

class Point {

static int x = 2;

}

class Test extends Point {

public static void main(String[] args) {

new Test().printX();

}

void printX() {

System.out.println(x + " " + super.x);

}

}

then the field

x

 of class

Point

 is no longer hidden within class

Test

; instead, the

simple name

x

 now refers to the field

Point.x

. Code in class

Test

 may still refer

to that same field as

super.x

. Therefore, the output from this variant program is:

2 2

8.3.3.2

Example: Hiding of Instance Variables

This example is similar to that in the previous section, but uses instance variables

rather than static variables. The code:

151