What is the meaning of “this” in Java?

Question

Normally, I use this in constructors only.

I understand that it is used to identify the parameter variable (by using this.something), if i

Answer 1

It's "a reference to the object in the current context" effectively. For example, to print out "this object" you might write:

System.out.println(this);

Note that your usage of "global variable" is somewhat off... if you're using this.variableName then by definition it's not a global variable - it's a variable specific to this particular instance.