CLASSES

Constructor Overloading

8.6.6

class ColoredPoint extends Point {

static final int WHITE = 0, BLACK = 1;

int color;

ColoredPoint(int x, int y) {

this(x, y, WHITE);

}

ColoredPoint(int x, int y, int color) {

super(x, y);

this.color = color;

}

}

the first constructor of

ColoredPoint

 invokes the second, providing an additional

argument; the second constructor of

ColoredPoint

 invokes the constructor of its

superclass

Point

, passing along the coordinates.

An explicit constructor invocation statement may not refer to any instance

variables or instance methods declared in this class or any superclass, or use

this

or

super

 in any expression; otherwise, a compile time error occurs. For example,

if the first constructor of

ColoredPoint

 in the example above were changed to:

ColoredPoint(int x, int y) {

this(x, y, color);

}

then a compile time error would occur, because an instance variable cannot be

used within a superclass constructor invocation.

An invocation of the constructor of the direct superclass, whether it actually

appears as an explicit constructor invocation statement or is provided automati 

cally ( 8.6.7), performs an additional implicit action after a normal return of con 

trol from the constructor: all instance variables that have initializers are initialized

at that time, in the textual order in which they appear in the class declaration. An

invocation of another constructor in the same class using the keyword

this

 does

not perform this additional implicit action.

 12.5 describes the creation and initialization of new class instances.

8.6.6   Constructor Overloading

Overloading of constructors is identical in behavior to overloading of methods.

The overloading is resolved at compile time by each class instance creation

expression ( 15.8).

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