There can be a lot of usage of this keyword. In java, this is a reference variable that refers to the current object
Usage of this keyword:
Here is given the 6 usage of this keyword:
| a) this keyword can be used to refer
current class instance variable. b) this() can be used to invoke current class constructor. c) this keyword can be used to invoke current class method (implicitly) d) this can be passed as an argument in the method call. e) this can be passed as argument in the constructor call. f) this keyword can also be used to return the current class instance. |
The this keyword can be used to refer current
class instance variable.
If there is ambiguity between the instance variable and parameter, this keyword
resolves the problem of ambiguity.
Understanding the problem without this keyword
Let's understand the problem if we don't use this keyword by the example given
below:
|
class employee{ int id; String name; employee(int id,String name){ id = id; name = name; } void display(){System.out.println(id+" "+name);} public static void main(String args[]){ employee e1 = new employee(111,"aman"); employee e2 = new employee(321,"Arzoo"); e1.display(); e2.display(); } } output:0 null; 0 null; |
In the above example, parameter (formal arguments) and
instance variables are same that is why we are using this keyword to distinguish
between local variable and instance variable.
Solution of the above problem by this keyword:-
example:-
|
class employee{ int id; String name; employee(int id,String name){ this.id = id; this.name = name; } void display(){System.out.println(id+" "+name);} public static void main(String args[]){ employee e1 = new employee(100,"aman"); employee e2 = new employee(200,"Arzoo"); e1.display(); e2.display(); } } output: 100 aman; 200 arzoo;
|
this() can be used to invoked current class
constructor.
The this() constructor call can be used to invoke the current class constructor
(constructor chaining). This approach is better if you have many constructors in
the class and want to reuse that constructor.
example:
|
class employee{ int id; String name; employee (){System.out.println("default constructor is invoked");} employee(int id,String name){ this ();//it is used to invoked current class constructor. this.id = id; this.name = name; } void display(){System.out.println(id+" "+name);} public static void main(String args[]){ employee e1 = new employee(100,"prag"); employeet e2 = new employee(200,"sonya"); e1.display(); e2.display(); } } Output: default constructor is
invoked |