Google Gauva API in a one glance: Composite Function

Guava API provide a way to apply series of functions on the given collection using Functions.compose

public static <A,B,C> Function<A,C> compose(Function<B,C> g,
                                            Function<A,? extends B> f)

Returns the composition of two functions. For f: A->B and g: B->C, composition is defined as the function h such that h(a) == g(f(a)) for each a.

Parameters:

g - the second function to apply

f - the first function to apply

Returns:

the composition of f and g

to test it further please follow my blog entry and add one method to the GuavaFunctionDemo class and run it

/**
 * 
 */
package com.rajkrrsingh.test.guava;

import java.util.Collection;
import java.util.Iterator;

import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.collect.Collections2;

/**
 * @author rks
 * @04-Jan-2015
 */
public class GuavaFunctionDemo {

	public static void main(String[] args) {
		//printEmployeeInUpperCase();
		printResultofCompositeFunction();
	}

	// Transformation of one collection to the other collection using Guava function
	public static void printEmployeeInUpperCase(){
		Collection<String> upperCaseEmpName = Collections2.transform(Employee.getEmployeeList(),new Function<Employee, String>() {

			@Override
			public String apply(Employee emp) {
				if(emp != null)
					return emp.getEmpName().toUpperCase();
				return "";

			}
		});

		Iterator<String> itr = upperCaseEmpName.iterator();
		while(itr.hasNext()){
			System.out.println(itr.next());
		}
	}

	// Apply a series of transformation by compostion of function
	public static void printResultofCompositeFunction(){
		Function<Employee, String> upperCaseEmpName = new Function<Employee, String>() {

			@Override
			public String apply(Employee emp) {
				if(emp!=null)
					return emp.getEmpName().toUpperCase();
				return "";
			}
		};

		Function<String, String> reverseEmpName = new Function<String, String>() {

			@Override
			public String apply(String empName) {
				if (empName!=null) {
					return new StringBuilder(empName).reverse().toString();
				}
				return "";
			}

		};
		;
		Collection<String> upperReverseCollection = Collections2.transform(Employee.getEmployeeList(), Functions.compose(reverseEmpName, upperCaseEmpName));

		Iterator<String> itr = upperReverseCollection.iterator();
		while(itr.hasNext()){
			System.out.println(itr.next());
		}
	}

}

you can see here we have applied two function here, the first on is to change element of the collection in uppercase and then reverse it.

Result:

SKR
KERED
KCAJ
KCIN