Tips of Functional Programing in Java

There are only some concepts, details should google yourself.

1. What is Functional Programing?
   • In mathematics, function is an expression that relates an input set to an output set.
   • Functional programming is a style of writing computer programs that treat computations as evaluating mathematical functions.
2. Lambda Calculus
   • Lambda calculus is a universal model, a formal system to express computations based on functional abstraction.
   • Tremendous impact : functional programing languages implements lambda calculus.
3. Concepts of functional programing
   1. First-Class and High-Order functions
   2. Pure functions
   3. Immutability
   4. Referential transparency
4. Functional programing techniques
   1. Composition : compose(), andThen()
   2. Monads :
      • a monad allows us to wrap a value, apply a set of transformations, and get the value back with all transformations applied。
      • such as : optional、stream、future etc, those have flatMap() method we call monad.
   3. Currying
      • Currying is a mathematical technique of converting a function that takes multiple arguments into a sequence of functions that take a single argument.
      • depends on : lambda expression and closures.
      • closures : Java has a limitation that variables the enclosing scope have to be final or effectively final.
   4. Recursion

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