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---
## Intent
Compose objects into tree structures to represent part-whole
hierarchies. Composite lets clients treat individual objects and compositions
of objects uniformly.
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients
treat individual objects and compositions of objects uniformly.
## Explanation
Real world example
> Every sentence is composed of words which are in turn composed of characters. Each of these objects is printable and they can have something printed before or after them like sentence always ends with full stop and word always has space before it
> Every sentence is composed of words which are in turn composed of characters. Each of these
> objects is printable and they can have something printed before or after them like sentence always
> ends with full stop and word always has space before it.
In plain words
@ -25,11 +27,16 @@ In plain words
Wikipedia says
> In software engineering, the composite pattern is a partitioning design pattern. The composite pattern describes that a group of objects is to be treated in the same way as a single instance of an object. The intent of a composite is to "compose" objects into tree structures to represent part-whole hierarchies. Implementing the composite pattern lets clients treat individual objects and compositions uniformly.
> In software engineering, the composite pattern is a partitioning design pattern. The composite
> pattern describes that a group of objects is to be treated in the same way as a single instance of
> an object. The intent of a composite is to "compose" objects into tree structures to represent
> part-whole hierarchies. Implementing the composite pattern lets clients treat individual objects
> and compositions uniformly.
**Programmatic Example**
Taking our sentence example from above. Here we have the base class and different printable types
Taking our sentence example from above. Here we have the base class `LetterComposite` and the
different printable types `Letter`, `Word` and `Sentence`.
```java
public abstract class LetterComposite {
@ -102,7 +109,7 @@ public class Sentence extends LetterComposite {
}
```
Then we have a messenger to carry messages
Then we have a messenger to carry messages:
```java
public class Messenger {
@ -143,7 +150,7 @@ public class Messenger {
}
```
And then it can be used as
And then it can be used as:
```java
var orcMessage = new Messenger().messageFromOrcs();
@ -153,13 +160,16 @@ elfMessage.print(); // Much wind pours from your mouth.
```
## Class diagram
![alt text](./etc/composite.urm.png "Composite class diagram")
## Applicability
Use the Composite pattern when
* you want to represent part-whole hierarchies of objects
* you want clients to be able to ignore the difference between compositions of objects and individual objects. Clients will treat all objects in the composite structure uniformly
* You want to represent part-whole hierarchies of objects.
* You want clients to be able to ignore the difference between compositions of objects and
individual objects. Clients will treat all objects in the composite structure uniformly.
## Real world examples