java8流编程

import java.util.List;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamDemo4 {

	public static void main(String[] args) {
		String str = "my name is 007";

		// 使用并行流
		str.chars().parallel().forEach(i -> System.out.print((char) i));
		System.out.println();
		// 使用 forEachOrdered 保证顺序
		str.chars().parallel().forEachOrdered(i -> System.out.print((char) i));

		// 收集到list
		List<String> list = Stream.of(str.split(" "))
				.collect(Collectors.toList());
		System.out.println(list);

		// 使用 reduce 拼接字符串
		Optional<String> letters = Stream.of(str.split(" "))
				.reduce((s1, s2) -> s1 + "|" + s2);
		System.out.println(letters.orElse(""));

		// 带初始化值的reduce
		String reduce = Stream.of(str.split(" ")).reduce("",
				(s1, s2) -> s1 + "|" + s2);
		System.out.println(reduce);

		// 计算所有单词总长度
		Integer length = Stream.of(str.split(" ")).map(s -> s.length())
				.reduce(0, (s1, s2) -> s1 + s2);
		System.out.println(length);

		// max 的使用
		Optional<String> max = Stream.of(str.split(" "))
				.max((s1, s2) -> s1.length() - s2.length());
		System.out.println(max.get());

		// 使用 findFirst 短路操作
		OptionalInt findFirst = new Random().ints().findFirst();
		System.out.println(findFirst.getAsInt());
	}

}

import java.util.List;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamDemo4 {

	public static void main(String[] args) {
        // 调用parallel 产生一个并行流
		IntStream.range(1, 100).parallel().peek(StreamDemo5::debug).count();
	}
	public static void debug(int i) {
		System.out.println(Thread.currentThread().getName() + " debug " + i);
        TimeUnit.SECONDS.sleep(3);
	}

}

        // 线程名字 : ForkJoinPool-1
		ForkJoinPool pool = new ForkJoinPool(20);
		pool.submit(() -> IntStream.range(1, 100).parallel()
				.peek(StreamDemo5::debug).count());
		pool.shutdown();
		
		synchronized (pool) {
			try {
				pool.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;

import org.apache.commons.collections4.MapUtils;

/**
 * 学生 对象
 */
class Student {
	/**
	 * 姓名
	 */
	private String name;

	/**
	 * 年龄
	 */
	private int age;

	/**
	 * 性别
	 */
	private Gender gender;

	/**
	 * 班级
	 */
	private Grade grade;

	public Student(String name, int age, Gender gender, Grade grade) {
		super();
		this.name = name;
		this.age = age;
		this.gender = gender;
		this.grade = grade;
	}

	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 Grade getGrade() {
		return grade;
	}

	public void setGrade(Grade grade) {
		this.grade = grade;
	}

	public Gender getGender() {
		return gender;
	}

	public void setGender(Gender gender) {
		this.gender = gender;
	}

	@Override
	public String toString() {
		return "[name=" + name + ", age=" + age + ", gender=" + gender
				+ ", grade=" + grade + "]";
	}

}

/**
 * 性别
 */
enum Gender {
	MALE, FEMALE
}

/**
 * 班级
 */
enum Grade {
	ONE, TWO, THREE, FOUR;
}

public class CollectDemo {

	public static void main(String[] args) {
		// 测试数据
		List<Student> students = Arrays.asList(
				new Student("小明", 10, Gender.MALE, Grade.ONE),
				new Student("大明", 9, Gender.MALE, Grade.THREE),
				new Student("小白", 8, Gender.FEMALE, Grade.TWO),
				new Student("小黑", 13, Gender.FEMALE, Grade.FOUR),
				new Student("小红", 7, Gender.FEMALE, Grade.THREE),
				new Student("小黄", 13, Gender.MALE, Grade.ONE),
				new Student("小青", 13, Gender.FEMALE, Grade.THREE),
				new Student("小紫", 9, Gender.FEMALE, Grade.TWO),
				new Student("小王", 6, Gender.MALE, Grade.ONE),
				new Student("小李", 6, Gender.MALE, Grade.ONE),
				new Student("小马", 14, Gender.FEMALE, Grade.FOUR),
				new Student("小刘", 13, Gender.MALE, Grade.FOUR));

		// 得到所有学生的年龄列表
		// s -> s.getAge() --> Student::getAge , 不会多生成一个类似 lambda$0这样的函数
		Set<Integer> ages = students.stream().map(Student::getAge)
				.collect(Collectors.toCollection(TreeSet::new));
		System.out.println("所有学生的年龄:" + ages);

		// 统计汇总信息
		IntSummaryStatistics agesSummaryStatistics = students.stream()
				.collect(Collectors.summarizingInt(Student::getAge));
		System.out.println("年龄汇总信息:" + agesSummaryStatistics);

		// 分块
		Map<Boolean, List<Student>> genders = students.stream().collect(
				Collectors.partitioningBy(s -> s.getGender() == Gender.MALE));
		// System.out.println("男女学生列表:" + genders);
		MapUtils.verbosePrint(System.out, "男女学生列表", genders);

		// 分组
		Map<Grade, List<Student>> grades = students.stream()
				.collect(Collectors.groupingBy(Student::getGrade));
		MapUtils.verbosePrint(System.out, "学生班级列表", grades);

		// 得到所有班级学生的个数
		Map<Grade, Long> gradesCount = students.stream().collect(Collectors
				.groupingBy(Student::getGrade, Collectors.counting()));
		MapUtils.verbosePrint(System.out, "班级学生个数列表", gradesCount);

	}

}