Not getting the use of 'this' keyword in constructor as shortcut approach.

Question

class Box{
int width;
int height;
int depth;
Box(){ //no-arg constructor
Width =1;
Height = 2;
Depth = 3;
Box(int width){
this.width = width;
height = 2;
depth = 3;
Box(int width, int height){
this.width = width;
this.height = height;
depth = 3;
/*Box(int width, int height, int depth){
this.width = width;
this.height = height;
this.depth = depth;
*//short cut approach*
*Box(int width, int height, int depth){*
this(width, height); //calls matching constructor from the same class
this.depth = depth;
Box(Box b){
this.width = b.width;
this.height = b.height;
this.depth = b.depth;
public class ConstructorDemo {
public static void main(String[] args) {
Box b1 = new Box(1,2,3);
Box b2 = new Box(b1);
In the above example, 'this' pointing to current object is understood but
this(width, height); is used instead of this.width=width; this.height=height;
how can it be shortcut when we have declared constructors ? And really how its so useful in a big code?
Edited by: 1010533 on Jun 7, 2013 12:54 PM

Answer 1

Welcome to the forum!
>
class Box{
int width;
int height;
int depth;
Box(){ //no-arg constructor
Width =1;
Height = 2;
Depth = 3;
Box(int width){
this.width = width;
height = 2;
depth = 3;
Box(int width, int height){
this.width = width;
this.height = height;
depth = 3;
/*Box(int width, int height, int depth){
this.width = width;
this.height = height;
this.depth = depth;
//short cut approach
Box(int width, int height, int depth){
this(width, height); //calls matching constructor from the same class
this.depth = depth;
Box(Box b){
this.width = b.width;
this.height = b.height;
this.depth = b.depth;
public class ConstructorDemo {
public static void main(String[] args) {
Box b1 = new Box(1,2,3);
Box b2 = new Box(b1);
In the above example, 'this' pointing to current object is understood but
this(width, height); is used instead of this.width=width; this.height=height;
how can it be shortcut when we have declared constructors ?
>
Shortcut? Who said it is a shortcut?
>
And really how its so useful in a big code?
>
EXTREMELY useful - especially in 'big code' (whatever you mean by that).
Constructors are meant to create VALID instances. The business rules for creating a valid instance may not be as simple as your example.
Ideally code should be written once and used often. The use of constructors is no different.
Once you have a contructor for a given set of arguments you should use it if you need to construct an instance like that.
So when you need a constructor that uses those same arguments and then some additional ones your new constructor should call the existing constructor and should then apply the new logic needed for the new constructor.
That is important because it means that the business logic needed for those two arguments is only implemented in ONE place. That logic might be very complicated and there is no valid reason to duplicate it.
Once you have a piece of code that works reuse it whenever possible.