6.15. This¶
Don’t worry, I’m not the only Java programmer to ask this question. In fact, this is such a common problem in object oriented programming that the Java standard library contains a special word that engineers can use when they are trying to differentiate their class attribute names from their constructor or method parameter names.
This keyword is called this. As the name suggests, this is used to describe the current object in a constructor or a method. Here is our Celebrity class again:
class Celebrity{
String name;
int age;
String type;
boolean isAlive;
public Celebrity(String name, int age, String type, boolean status){
this.name = name;
this.age = age;
this.type = type;
isAlive = status;
System.out.println("A new celebrity has been created!");
}
}
Gasp! The dot operator strikes again! In this case, this is being used as the “objectReference” and is explicitly referring to the object that is actively being made by the constructor. We know that this object has attributes name, age, type and isAlive, and that we are initializing them to the values passed in for our parameters name, age, type and status.
If we did not use this for the assignment of our first three attributes, our computer would not know which name, age, or type you are referring to; is it the attribute or the parameter? This is not a problem for the attribute isAlive because the parameter we are using within the assignment statement is status, not isAlive. We’re lucky that I was able to come up with a more appropriate name for this last parameter! It may help to know that our compiler secretly plugs in the keyword this for our final assignment statement, even though it wasn’t explicitly written. You can add this yourself if you’d like, though programmers prefer to only break out this when there are naming conflicts between class attributes and the parameters of a constructor a method.
class Celebrity{
String name;
int age;
String type;
boolean isAlive;
public Celebrity(String name, int age, String type, boolean status){
this.name = name;
this.age = age;
this.type = type;
this.isAlive = status;
System.out.println("A new celebrity has been created!");
}
}
The keyword this can be used in other situations, though the problem described above is by far the most common use in this course.