SupplierFunctionalInterfaceTest.java

package suppliers;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.equalTo;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.junit.Test;

public class SupplierFunctionalInterfaceTest {

	@Test
	public void shouldGetTheTextByUsingSupplierWithoutLambdaExpression() throws Exception {
		Supplier<String> supplier = new Supplier<String>() {

			@Override
			public String get() {
				return "Java 8 - Supplier by Craft Coder";
			}
		};
		
		String guide = supplier.get();
		
		assertThat(guide, equalTo("Java 8 - Supplier by Craft Coder"));
	}
	
	@Test
	public void shouldGetTheTextByUsingSupplierWithLambdaExpression() throws Exception {
		Supplier<String> supplier = () -> "Java 8 - Supplier by Craft Coder";
		
		String guide = supplier.get();
		
		assertThat(guide, equalTo("Java 8 - Supplier by Craft Coder"));
	}
	
	@Test
	public void shouldGetAListOfRandomNumbersByUsingLoops() throws Exception {
		List<Integer> randomNumbers = new ArrayList<>();
		for (int i = 0; i < 10; i++) {
			Integer number = RandomNumbers.getNext();
			randomNumbers.add(number);
		}
		
		System.out.println(randomNumbers);
	}
	
	@Test
	public void shouldGetAListOfRandomNumbersGreaterThan5ByUsingLoops() throws Exception {
		List<Integer> randomNumbers = new ArrayList<>();
		for (int i = 0; i < 10; i++) {
			Integer number = RandomNumbers.getNext();
			if (number > 5) {
				randomNumbers.add(number);
			}
		}
		
		System.out.println(randomNumbers);
	}
	
	@Test
	public void shouldGetAListOfRandomNumbersByUsingSupplier() throws Exception {
		Supplier<Integer> supplier = () -> RandomNumbers.getNext();
		
		List<Integer> randomNumbers = Stream
			.generate(supplier)
			.filter(number -> number > 5)
			.limit(10)
			.collect(Collectors.toList());

		System.out.println(randomNumbers);
	}
	
}

class RandomNumbers {
	
	public static Integer getNext() {
		return new Random().nextInt(10);
	}
	
}