Java Aggregation (HAS-A)

Syntax

class ClassA {
    ClassB b;
    // ...
}

Example

class Car {
    Engine engine;
    // ...
}

class Engine {
    // ...
}

Output

Creating an instance of the Car class will also create an instance of the Engine class.

Explanation

In Java, aggregation (also known as "HAS-A" relationship) is a type of association between two classes where one class "HAS-A" reference to another class. This creates a relationship between the two classes.

In the example above, the Car class "HAS-A" reference to the Engine class. This means that when an instance of the Car class is created, an instance of the Engine class is also created. The Car class can then access the Engine class and its methods, as long as they are public or package-private.

Aggregation is useful for creating complex objects that have multiple parts. It allows for code reusability and enhances the readability of the code.

Use

Aggregation is used to create relationships between objects in Java. It is especially useful when creating complex objects that have multiple parts or when dealing with relationships between large numbers of objects.

Aggregation can also be used to create more modular and maintainable code. By breaking down larger objects into smaller, more manageable parts, it becomes easier to modify and maintain the code.

Important Points

• Aggregation is a type of association between two classes.
• In aggregation, one class "HAS-A" reference to another class.
• Aggregation is useful for creating complex objects with multiple parts.
• Aggregation promotes code reusability and enhances readability.
• Aggregation can be used to create more modular and maintainable code.

Summary

Aggregation is a type of association between two classes where one class "HAS-A" reference to another class. It is useful for creating complex objects with multiple parts and promotes code reusability. Aggregation allows for more modular and maintainable code and is a useful tool for creating relationships between objects in Java.