# Passing this as a method
**URL:** https://discourse.processing.org/t/passing-this-as-a-method/15796
**Category:** Beginners
**Created:** [November 25, 2019, 1:24pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796 "2019-11-25T13:24:12Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@paulgoux](https://discourse.processing.org/u/paulgoux)
#### Post date: [November 25, 2019, 1:24pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/1 "2019-11-25T13:24:12Z")
Controlp5 passes this as a method,
controlP5 = new ControlP5(this)
How do you create a class that can do this?
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [November 25, 2019, 1:41pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/2 "2019-11-25T13:41:47Z")
```auto
import processing.core.PApplet;
public class Library {
protected final PApplet p;
public Library(final PApplet pa) {
p = pa;
}
}
```
---
### Author:  [@paulgoux](https://discourse.processing.org/u/paulgoux)
#### Post date: [November 25, 2019, 1:56pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/3 "2019-11-25T13:56:14Z")
Does this allow you to retrieve all sketch events and variables? What are the limitations?
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [November 25, 2019, 2:07pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/4 "2019-11-25T14:07:34Z")
It’s restricted to PApplet’s members only: 😞
[Processing.GitHub.io/processing-javadocs/core/processing/core/PApplet.html](http://Processing.GitHub.io/processing-javadocs/core/processing/core/PApplet.html)
Beyond that, you’re gonna need to rely on reflection/inspection techniques: 😬
[Docs.Oracle.com/en/java/javase/11/docs/api/java.base/java/lang/reflect/package-summary.html](http://Docs.Oracle.com/en/java/javase/11/docs/api/java.base/java/lang/reflect/package-summary.html)
---
### Author:  [@Lexyth](https://discourse.processing.org/u/Lexyth)
#### Post date: [November 25, 2019, 5:24pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/5 "2019-11-25T17:24:41Z")
‚this‘ is a keyword refering to the instance of the object. It not only works with PApplet, but you can also do something like this :
```auto
class Test {
float a = 0;
Test () {
}
void setA( float a) {
this.a = a; // in this case ‚this‘ is used to differentiate between the classes variable ‚a’ and the methods parameter ‚a‘
// Generally you don‘t need this in Processing, because it is implied, but there can be moments when you need it.
}
//But you could also do something nonsensical like this
Test getThis() {
return this; //that makes no sense, because you‘d need a reference to this objects instance
// to even call this method that just returns a reference to this Objects instance
// but maybe there might be a use for that...
}
}
```
Generally ‚this‘ is a reference to the instance of the class it is called within.
In your case, it is called within the PApplet, and thus gives back a reference to your current PApplet, so that controlP5 can reference it.
It‘s often needed if you have to communicate with external classes.
---
### Author:  [@jeremydouglass](https://discourse.processing.org/u/jeremydouglass)
#### Post date: [December 3, 2019, 7:25pm UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/6 "2019-12-03T19:25:19Z")
> [@Lexyth](#):
>
> ```auto
> //But you could also do something nonsensical like this
> Test getThis() {
> return this;
> [...]
> // but maybe there might be a use for that...
>
> ```
Returning `this` (the object self-reference) is actually common to do in method chaining – e.g. in fluent interfaces.
> **[Method chaining](https://en.wikipedia.org/wiki/Method_chaining)**
>
> Method chaining is a common syntax for invoking multiple method calls in object-oriented programming languages. Each method returns an object, allowing the calls to be chained together in a single statement without requiring variables to store the intermediate results.
> Local variable declarations are syntactic sugar.
> Method chaining eliminates an extra variable for each intermediate step. The developer is saved from the cognitive burden of naming the variable and keeping the variable in mind.
- [Fluent interface - Wikipedia](https://en.wikipedia.org/wiki/Fluent_interface)
So:
```auto
/**
* Method chaining example
* 2019-12 Jeremy Douglass -- Processing 3.4
*/
class Test {
Test be(){
print("be ");
return this;
}
Test go(){
print("go ");
return this;
}
Test say(String s){
print(s);
return this;
}
}
Test t = new Test();
t.go().be().say("done!");
// go be done!
```
---
### Author:  [@Lexyth](https://discourse.processing.org/u/Lexyth)
#### Post date: [December 4, 2019, 2:32am UTC](https://discourse.processing.org/t/passing-this-as-a-method/15796/7 "2019-12-04T02:32:54Z")
Ohhh, that is awesome 😅
I didn‘t know that was a thing, though thinking about it now, it sure makes sense 😅
Thanks 😊