Java8 | Function

What we need to know about Function

• Function is in the package java.util.function
• Function interface is -> public interface Function<T, R>
• It is combined with the map method found in the stream,
  The map () function is a method in the Stream class that represents a functional programming concept. In simple words, the map () is used to transform one object into another by applying a function.
  For example, by using the map () function, you can convert a list of String into a List of Integer by applying the Integer.valueOf () method to each String on the input list.
• Function methods are below,
  R apply(T t);
  <V> Function<V, R> compose(Function<? super V, ? extends T> before)
  <V> Function<T, V> andThen(Function<? super R, ? extends V> after)
  <T> Function<T, T> identity()
• We will investigate these methods,

Java 8 code example showing usage of Function.apply() method;

FunctionTest01.java

• We define Function in 9. and 10. lines,
• We call apply() method in 13,14,15. lines and then we see results,

Another example below

FunctionTest02.java

Another example;

FunctionTest03.java

• We define Function<Employee, String> , Its means we give Employee and it returns String
• e-> e.getName() . It takes as input an Employee object and returns his\her name, which is a String value, as output.

Another example,

FunctionTest04.java

• You can use it while you call the method,

Java 8 code example showing usage of Function.andThen() method;

FunctionTest05.java

• We defined 2 functions 3,4. lines.
• İf you use compose, you should be careful because compose firstly start within and then makes outside.
• We can combine 2 functions like 6. line

Github: Function