There are a couple of important concepts in this question:
1. Within an instance method, you can access the current object of the same class using 'this'. Therefore, when you access this.myValue, you are accessing the instance member myValue of the ChangeTest instance.
2. If you declare a local variable (or a method parameter) with the same name as the instance field name, the local variable "shadows" the member field. Ideally, you should be able to access the member field in the method directly by using the name of the member (in this example, myValue). However, because of shadowing, when you use myValue, it refers to the local variable instead of the instance field.

Within the showOne() method, there are two variables accessible with the same name myValue. One is the method parameter and another is the member field of ChangeTest object. Ideally, you should be able to access the member field in the method directly by using the name myValue but in this case, the method parameter shadows the member field because it has the same name. So when you use myValue, you are actually using the method parameter instead of the member field.

Now, in showTwo(), you are assigning the value contained in myValue (i.e. 200) to this.myValue, which is the instance member.  Therefore, in the next line, when you print ct.myValue, it prints 200.