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Lesson 7: Functional Interfaces, Lambda Expressions, Method References
By
lunauii
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Topics Covered
- Functional Interfaces
- Lambda Expressions
- Method References
All of these only available after JRE/JDK 8.
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Functional Interfaces
An interface which only has a single abstract method. Can have default and static methods.
Can declare with @FunctionalInterface (optional, but highly recommended for clarity)
Java automatically knows what types, parameters, and return type the interface implements due to there only being one abstract method. Due to this, @Override is not necessary and it can be implemented just by using a lambda expression.
See Java interface Consumer<T>.
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Lambda Expressions
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Method References
Method references are a shorthand syntax which can replace lambda expressions.
Method references use the :: operator without any parameters.
Class::staticMethod is an alternative to the lambda expression (args) -> Class.staticMethod(args).
- Can be used to make simple lambda expressions by making use of existing methods
- Should be used over lambda expressions when there are more complex/repetitive tasks
/*
* Given an ArrayList<String> called names...
*/
// Example 1
names.forEach(System.out::println);
// Example 2; given methods in School
names.forEach(School::printStrLen);
names.forEach(School::printReverse);
Notice the :: in the examples.