Custom annotation processing while coding - annotations

Question

The purpose of the project I'm working on is to handle annotation at compile time, it is not focused on what exactly I'm developing.
I took a simple subject for this and I'm writing a custom collection that will store elements and provide methods to manage them.
What I wanna do is to create an annotation #Contains, for example, to generate itemsContains method that could be processed while coding (instead of writing code manually).
public class Array {
private List<String> items;
public Array() {
items = Arrays.asList("abc", "def", "xyz");
}
public boolean itemsContains(String expected) {
return items.contains(expected);
}
}
Generally, I want my class to look something like:
public class Array {
#Contains
private List<String> items;
public Array() {
items = Arrays.asList("abc", "def", "111");
}
}
The important thing I want to reach is to have itemsContains method show up once the annotation is applied to a field. This is how it should look like:
expected result
Alternate existing examples are Lombok's #Getter/#Setter.
So what functionality or configurations should I implement to get the expected result?
Would be grateful for some real implementations or guides how to perform it step by step.

Answer 1

Annotation processing does not change the source file yet it generates a new file,
Lombok on the other hand does a trick to modify the source file itself, meaning that you need to call the generated class somewhere in your code.
One way to do this is to generate a class that extends the main class
#Generated
public class ArrayProxy extends Array {
public boolean itemsContains(String expected) {
return items.contains(expected);
}
}
and in your main class you need to do two things:
first you need to make items protected
you can add factory method to actually create the generated class
public class Array {
#Contains
protected List<String> items;
public static ArrayProxy create(){
return new ArrayProxy();
}
private Array() {
items = Arrays.asList("abc", "def", "111");
}
}
And of course you need to use it like this
ArrayProxy array = Array.create();
array.itemsContains("expected");