Usage of
Function, Method Reference and Closure in functional programming
package com.java8.chapter3;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import
java.util.function.ToIntFunction;
/* Example of
Function<R,T> interface i.e. Converting an object from one DT to another
DT
* Use of Closure in lamda and anonymous
inner class
* Use of Method Reference, replacement of lamda
* R apply(T t);
*/
public class FunctionLamda {
public static void main(String[] args) {
List<Integer> list = Arrays.asList(2, 4,
6, 8);
// Printing
list<Integer>
list.stream().forEach(p -> System.out.println(p));
// perform any operation on
each element of list and print
System.out.println(performOperation(list,p->p*2));
// Create new Integer
list(length of String) from list of Strings using Function<String,Integer>
System.out.println(extractOperation(Arrays.asList("Paras","Suriender","Sham"), s->s.length()));
// Create new Integer
list(length of String) from list of Strings using ToIntFunction<String>
System.out.println(extractOperation2(Arrays.asList("Paras","Suriender","Sham"), s->s.length()));
/* Lamda and annonymous
function accessing variables outside of local space
* Closure -a closure is an
instance of a function that can reference nonlocal variables of that
function with no restrictions
*/
int a=10,b=20;
Thread thread1 = new Thread(new Runnable() {
public void run() {
System.out.println(a+b);
}
});
thread1.start();
Thread thread = new Thread(()-> System.out.println(a));
thread.start();
Function<String, Integer>
stringToInteger =(String s) -> Integer.parseInt(s);
System.out.println(stringToInteger.apply("12346"));
// Method Reference , Class
:: static method
Function<String, Integer>
stringToInteger2 =Integer::parseInt;
System.out.println(stringToInteger2.apply("4123"));
}
public static List<Integer>
performOperation(List<Integer> list,
Function<Integer, Integer> function) {
List<Integer> result = new ArrayList<Integer>();
for(Integer p : list){
result.add(function.apply(p));
}
return result;
}
public static List<Integer>
extractOperation(List<String> list,
Function<String, Integer> function) {
List<Integer> result = new ArrayList<Integer>();
for(String p : list){
result.add(function.apply(p));
}
return result;
}
public static List<Integer> extractOperation2(List<String>
list, ToIntFunction<String> function) {
List<Integer> result = new ArrayList<Integer>();
for(String p : list){
result.add(function.applyAsInt(p));
}
return result;
}
}
Output:
2 4 6 8
[4, 8,
12, 16]
[5, 9,
4]
[5, 9,
4]
30
10
12346
4123
