Google Gauva API in a one glance: Predicate

• Predicate<T>, which has the single method boolean apply(T input). Instances of Predicate are generally expected to be side-effect-free and consistent with equals.

@GwtCompatible
public interface Predicate<T>

Determines a true or false value for a given input.The Predicates class provides common predicates and related utilities.

lets see how to use predicate to filter out some elements from the given collection. create a tester class as follows and follow along my blog post to get Employee Class

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

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

import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.Collections2;
import com.google.common.collect.Iterables;

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

	public static void main(String[] args) {
		pridcateDemo();
	}

	public static void pridcateDemo(){
		List<Employee> empList = Employee.getEmployeeList();

		Predicate<Employee> ageOver30 = new Predicate<Employee>() {

			@Override
			public boolean apply(Employee emp) {
				if(emp.getAge()>30){
					return true;
				}
				return false;
			}
		};

		Predicate<Employee> slryLt10000 = new Predicate<Employee>() {

			@Override
			public boolean apply(Employee emp) {
				if(emp.getSalary()<10000)
					return true;
				return false;
			}
		};

		System.out.println("**** print emp name whose age is greater than 30 ****");
		Iterator<Employee> filterAgeIterator= Iterables.filter(empList, ageOver30).iterator();
		while(filterAgeIterator.hasNext()){
			System.out.println(filterAgeIterator.next().getEmpName());
		}

		System.out.println("**** print emp name whose age is greater than 30 and salary is less than 10000 ****");
		Iterator<Employee> filterOnAgeAndSal= Iterables.filter(empList, Predicates.and(ageOver30, slryLt10000)).iterator();
		while(filterOnAgeAndSal.hasNext()){
			System.out.println(filterOnAgeAndSal.next().getEmpName());
		}

		System.out.println("**** print emp name whose age is greater than 30 OR salary is less than 10000 ****");
		Iterator<Employee> filterOnAgeORSal= Iterables.filter(empList, Predicates.or(ageOver30, slryLt10000)).iterator();
		while(filterOnAgeORSal.hasNext()){
			System.out.println(filterOnAgeORSal.next().getEmpName());
		}
	}
}

Please follow my comments in the code to relate with the output

**** print emp name whose age is greater than 30 ****
RKS
Derek
Nick
**** print emp name whose age is greater than 30 and salary is less than 10000 ****
Nick
**** print emp name whose age is greater than 30 OR salary is less than 10000 ****
RKS
Derek
Jack
Nick