Item Prefer the use of standard functional interfaces

Evolution of APIs with Lambdas: With the introduction of lambdas in Java, practices for writing APIs have changed, such as avoiding the Template Method pattern in favor of static factories or constructors that accept function objects.

LinkedHashMap example: Instead of overriding the removeEldestEntry method for cache control, it would be more modern to use a static factory or constructor with a function object, using the BiPredicate functional interface.

Usage of Standard Functional Interfaces: The java.util.function package offers a wide collection of standard functional interfaces, which should be preferred over custom interfaces to make the API easier to understand and improve interoperability.

Main Functional Interfaces:

• UnaryOperator: Applies a function of type T to T.
• BinaryOperator: Applies a two-argument function of type T to T.
• Predicate: Tests an argument and returns a boolean.
• Function: Applies a function of type T to R.
• Supplier: Provides a value of type T with no arguments.
• Consumer: Consumes an argument of type T without return.

Functional Interfaces for Primitive Types: There are variants of the six basic interfaces for primitive types (int, long, double), such as IntPredicate and LongBinaryOperator.

When to Create Custom Functional Interfaces:
When no standard interface meets the needs.
When a descriptive name or strong contract is needed.
When the interface can benefit from custom default methods.
Use of the @FunctionalInterface Annotation: Indicates that the interface was designed to support lambdas, ensuring that it has only one abstract method.

Avoid Ambiguous Overloads: Do not create methods with many overloads that accept different functional interfaces in the same argument position to avoid ambiguities.

**Conclusion: **Lambdas and functional interfaces must be considered in the design of modern APIs. Generally, it is preferable to use the default java.util.function interfaces, except in specific cases that warrant custom interfaces.

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