The composition is a design technique in java to implement a has-a relationship. Java Inheritance is used for code reuse purposes and the same we can do by using inheritance. The composition is achieved by using an instance variable that refers to other objects. If an object contains the other object and the contained object cannot exist without the existence of that object, then it is called composition. In more specific words composition is a way of describing reference between two or more classes using instance variable and instance should be created before is used. To better understand how the composition works, let’s take the example of Library
Let’s understand the composition in Java with the example of books and library. In this example, we create a class Book that contains data members like author, and title and create another class Library that has a reference to refer the list of books. A library can have no. of books on the same or different subjects. So, If the Library gets destroyed then All books within that particular library will be destroyed. i.e., books can not exist without a library. The relationship between the library and books are composition.
Title : EffectiveJ Java and Author : Joshua Bloch Title : Thinking in Java and Author : Bruce Eckel Title : Java: The Complete Reference and Author : Herbert Schildt
Benefits of using Composition:
- Composition allows the reuse of code.
- Java doesn’t support multiple inheritances but by using composition we can achieve it.
- Composition offers better test-ability of a class.
- By using composition, we are flexible enough to replace the implementation of a composed class with a better and improved version.
- By using composition, we can also change the member objects at run time, to dynamically change the behavior of your program.
Key points of Composition in Java
- It represents a has-a relationship.
- In composition, both the entities are dependent on each other.
- When there is a composition between two entities, the composed object cannot exist without the other entity. For example, A library can have no. of books on the same or different subjects. So, If the Library gets destroyed then All books within that particular library will be destroyed. i.e., books can not exist without a library.
- The composition is achieved by using an instance variable that refers to other objects.
- We have to favor Composition over Inheritance.
Attention reader! Don’t stop learning now. Get hold of all the important Java and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.
- Association, Composition and Aggregation in Java
- Difference between Inheritance and Composition in Java
- Java.util.BitSet class methods in Java with Examples | Set 2
- Java.Lang.Float class in Java
- Java.io.BufferedInputStream class in Java
- Java.io.ObjectInputStream Class in Java | Set 1
- Java.util.BitSet class in Java with Examples | Set 1
- Java.io.File Class in Java
- Java.io.BufferedWriter class methods in Java
- Java.io.DataOutputStream in Java
- Java.io.StreamTokenizer Class in Java | Set 1
- Java.io.InputStream Class in Java
- Java.io.SequenceInputStream in Java
- Java.io.StreamTokenizer Class in Java | Set 2
- Java.io.Console class in Java
- Java.io.FilterOutputStream Class in Java
- Java.io.StringWriter class in Java
- Java.io.CharArrayReader Class in Java
- Java.io.FileInputStream Class in Java
- Java.io.CharArrayWriter class in Java | Set 1
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.