Java8新特性：Stream基本使用示例

实体类（示例用到的）：

public class Employee {

	private int id;
	private String name;
	private int age;
	private double salary;

	public Employee() {
	}

	public Employee(String name) {
		this.name = name;
	}

	public Employee(String name, int age) {
		this.name = name;
		this.age = age;
	}

	public Employee(int id, String name, int age, double salary) {
		this.id = id;
		this.name = name;
		this.age = age;
		this.salary = salary;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public String show() {
		return "测试方法引用！";
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		long temp;
		temp = Double.doubleToLongBits(salary);
		result = prime * result + (int) (temp ^ (temp >>> 32));
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Employee other = (Employee) obj;
		if (age != other.age)
			return false;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		if (Double.doubleToLongBits(salary) != Double.doubleToLongBits(other.salary))
			return false;
		return true;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", salary=" + salary + "]";
	}

}

Stream基本使用示例

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Stream;

import org.junit.Test;

/*
 * 一、Stream API 的操作步骤：
 * 
 * 1. 创建 Stream
 * 
 * 2. 中间操作
 * 
 * 3. 终止操作(终端操作)
 */
public class TestStreamaAPI {
	
	//1. 创建 Stream
	@Test
	public void test1(){
		//1. Collection 提供了两个方法  stream() 与 parallelStream()
		List<String> list = new ArrayList<>();
		Stream<String> stream = list.stream(); //获取一个顺序流
		Stream<String> parallelStream = list.parallelStream(); //获取一个并行流
		
		//2. 通过 Arrays 中的 stream() 获取一个数组流
		Integer[] nums = new Integer[10];
		Stream<Integer> stream1 = Arrays.stream(nums);
		
		//3. 通过 Stream 类中静态方法 of()
		Stream<Integer> stream2 = Stream.of(1,2,3,4,5,6);
		
		//4. 创建无限流
		//迭代
		Stream<Integer> stream3 = Stream.iterate(0, (x) -> x + 2).limit(10);
		stream3.forEach(System.out::println);
		
		//生成
		Stream<Double> stream4 = Stream.generate(Math::random).limit(2);
		stream4.forEach(System.out::println);
		
	}
	
	//2. 中间操作
	List<Employee> emps = Arrays.asList(
			new Employee(102, "李四", 59, 6666.66),
			new Employee(101, "张三", 18, 9999.99),
			new Employee(103, "王五", 28, 3333.33),
			new Employee(104, "赵六", 8, 7777.77),
			new Employee(104, "赵六", 8, 7777.77),
			new Employee(104, "赵六", 8, 7777.77),
			new Employee(105, "田七", 38, 5555.55)
	);
	
	/*
	  筛选与切片
		filter——接收 Lambda ， 从流中排除某些元素。
		limit——截断流，使其元素不超过给定数量。
		skip(n) —— 跳过元素，返回一个扔掉了前 n 个元素的流。若流中元素不足 n 个，则返回一个空流。与 limit(n) 互补
		distinct——筛选，通过流所生成元素的 hashCode() 和 equals() 去除重复元素
	 */
	
	//内部迭代：迭代操作 Stream API 内部完成
	@Test
	public void test2(){
		//所有的中间操作不会做任何的处理
		Stream<Employee> stream = emps.stream()
			.filter((e) -> {
				System.out.println("测试中间操作");
				return e.getAge() <= 35;
			});
		
		//只有当做终止操作时，所有的中间操作会一次性的全部执行，称为“惰性求值”
		stream.forEach(System.out::println);
	}
	
	//外部迭代
	@Test
	public void test3(){
		Iterator<Employee> it = emps.iterator();
		
		while(it.hasNext()){
			System.out.println(it.next());
		}
	}
	
	@Test
	public void test4(){
		emps.stream()
			.filter((e) -> {
				System.out.println("短路！"); // &&  ||
				return e.getSalary() >= 5000;
			}).limit(3)
			.forEach(System.out::println);
	}
	
	@Test
	public void test5(){
		emps.parallelStream()
			.filter((e) -> e.getSalary() >= 5000)
			.skip(2)
			.forEach(System.out::println);
	}
	
	@Test
	public void test6(){
		emps.stream()
			.distinct()
			.forEach(System.out::println);
	}
}