Why Use Interfaces Instead of Concrete Types Like ArrayList in Java?

Why Prefer Interfaces Over Concrete Types in Java

PMD often recommends utilizing interfaces instead of implementation types like 'ArrayList'. Consider the example below:

ArrayList<Object> list = new ArrayList<Object>();

PMD would flag this as a violation, suggesting the following correction:

List<Object> list = new ArrayList<Object>();

Why is using 'List' preferable to 'ArrayList'?

Employing interfaces over concrete types is essential for:

• Encapsulation: Interfaces hide the internal implementation, promoting better code organization and maintainability.
• Loose Coupling: By utilizing interfaces, classes are not directly dependent on specific implementations, allowing for easier code modifications in the future.

This approach is advantageous in several ways:

• Easier Unit Testing: Interfaces facilitate mocking techniques, making unit testing more straightforward.
• Flexible Implementation Changes: If the underlying implementation needs to be altered, doing so becomes less complex with interfaces.

Additionally, it's recommended to follow this practice in custom APIs to ensure flexibility and testability in the future.

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