The this
keyword is primarily used in three situations. The first and most common is in setter methods to disambiguate variable references. The second is when there is a need to pass the current class instance as an argument to a method of another object. The third is as a way to call alternate constructors from within a constructor.
Case 1: Using this
to disambiguate variable references. In Java setter methods, we commonly pass in an argument with the same name as the private member variable we are attempting to set. We then assign the argument x
to this.x
. This makes it clear that you are assigning the value of the parameter "name" to the instance variable "name".
public class Foo { private String name; public void setName(String name) { this.name = name; } }
Case 2: Using this
as an argument passed to another object.
public class Foo{ public String useBarMethod() { Bar theBar = new Bar(); return theBar.barMethod(this); } public String getName() { return "Foo"; } } public class Bar{ public void barMethod(Foo obj) { obj.getName(); } }
Case 3: Using this
to call alternate constructors. In the comments, trinithis correctly pointed out another common use of this
. When you have multiple constructors for a single class, you can use this(arg0, arg1, ...)
to call another constructor of your choosing, provided you do so in the first line of your constructor.
class Foo{ public Foo() { this("Some default value for bar"); //optional other lines } public Foo(String bar) { // Do something with bar }}
I have also seen this used to emphasize the fact that an instance variable is being referenced (sans the need for disambiguation), but that is a rare case in my opinion.
