Concstructors withing constructors

[Sumanth Shanbhag]

Hi All,

Could someone please tell me if we could have one constructor declared inside another constructor? What are its potential disadvantages and advantages, if any?

Regards,
Sumanth

[Keith Lynn]

No, you cannot have a method declared directly inside a method.

[marc weber]

You cannot "declare" or define a constructor within a constructor, but you can call another constructor from within a constructor.

Within a constructor, the keyword "this" along with the appropriate arguments can be used to call an overloaded version of the same constructor. The reason is usually to avoid code duplication. For example...

MyClass(int i) {
  //lots of code here to get object ready
}
 
MyClass(int i, String s) {
  this(i);//avoids duplication by calling int constructor
  //does something extra with String s
}

[Sumanth Shanbhag]

So, i guess one of the primary advantages of "this" keyword is code reusability?
Thanks Marc!

[Sidd Kulk]

'this' keyword is not meant for code reuse. It is just meant to refer the current object. When in a class, you call a non-static member from a non-static method, you need not prefix it with 'this.', because the compiler understands it. Though, for better readability, the keyword can be used.

Sid

[Jesper de Jong]

Originally posted by Keith Lynn:
No, you cannot have a method declared directly inside a method.

But this doesn't answer the question, because a constructor is not a method.

[Sumanth Shanbhag]

Sid,

Thanks for your inputs, but i was referring to Marc's answer.
He was talking about having "this" call another constructor from
within a constructor.

Regards,
Sumanth

[Keith Lynn]

Originally posted by Jesper Young:

But this doesn't answer the question, because a constructor is not a method.

Technically, no. But the principle is the same. The body of the constructor can't directly have a method declaration or constructor in it.

[marc weber]

Originally posted by Sumanth Shanbhag:
So, i guess one of the primary advantages of "this" keyword is code reusability? ...

Well, that's just one way to use "this" within a constructor (which I thought might relate to your question of a constructor "within" a constructor), but I don't think I would call it a "primary advantage." As pointed out above, "this" also references the calling instance, so it's often used in constructors to differentiate an instance variable from a local variable with the same name. For example...

class MyClass {
  int myInt; //instance variable
  MyClass(int myInt) {
    this.myInt = myInt; //set instance variable to value of local variable
  }
}