Its not a good example of the use of the "this" keyword. Typically you wouldn't do what you wrote, at least not in clean code.
"this" is used to pass the instance of the class to other functions. You can use the "this" keyword to reference the current instance of the class or pass to other subroutines, but you typically wouldn't use the "this" keyword to access data in the class you are working in. Its not a violation of the keyword, but just doesn't add any value.
[Edit]
I'm not sure if this is valid in Java, but in c# we can also use it in the following way:
class Myclass
{
String firstname;
public Myclass(String n1)
{
firstname=n1;
}
public Myclass(String firstname,String lastname)
{
this.firstname = firstname + " " + lastname;
}
}
To differentiate between the parameter and the class member.
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