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java8 新特性 Stream流 分组 排序 过滤 多条件去重

java 来源:anningx 3次浏览

java8 新特性 Stream流 分组 排序 过滤 多条件去重

public class Streams {
	
	private static List<User> list = new ArrayList<User>();
	
	public static void main(String[] args) {
		list =  Arrays.asList(
				new User(1, "a", 10),
				new User(4, "d", 19),
				new User(5, "e", 13),
				new User(2, "b", 14),
				new User(3, "a", 10),
				new User(6, "f", 16)
				);
		
		long start = System.currentTimeMillis();
		
		order();
		
		println(String.format("耗时[%s]毫秒", (System.currentTimeMillis() - start)));
		
	}
	
	/**
	 * 多条件去重
	 * @param list
	 */
	public static void order() {
		list.stream().collect(Collectors.collectingAndThen(
				Collectors.toCollection(() -> new TreeSet<>(
						Comparator.comparing(o -> o.getAge() + ";" + o.getName()))), ArrayList::new)).forEach(u -> println(u));
	}
	
	public static void group() {
		Map<Integer, List<User>> collect = list.stream().collect(Collectors.groupingBy(User::getAge));
		System.out.println(collect);
	}
	
	/**
	 * filter过滤
	 * @param list
	 */
	public static void filterAge() {
		list.stream().filter(u -> u.getAge() == 10).forEach(u -> println(u));
	}
	
	/**
	 * sorted排序
	 */
	public static void stord() {
		list.stream().sorted(Comparator.comparing(u-> u.getAge())).forEach(u -> println(u));
		
	}
	/**
	 * limit方法限制最多返回多少元素
	 */
	public static void limit() {
		list.stream().limit(2).forEach(u -> println(u));
	}
	/**
	 * 不要前多n个元素,n大于满足条件的元素个数就返回空的流
	 */
	public static void skip() {
		list.stream().skip(2).forEach(u -> println(u));
	}
	// 最大值 最小值
	public static void statistics() {
		Optional<User> min = list.stream().min(Comparator.comparing(User::getUserId));
		println(min);
		Optional<User> max = list.stream().max(Comparator.comparing(User::getUserId));
		println(max);
	}
	
	// 统计
	public static void summarizingInt(){
		IntSummaryStatistics statistics = list.stream().collect(Collectors.summarizingInt(User::getAge));
		double average = statistics.getAverage();
		long count = statistics.getCount();
		int max = statistics.getMax();
		int min = statistics.getMin();
		long sum = statistics.getSum();
		println(average);
		println(count);
		println(min);
		println(sum);
		println(max);
		
	}
	/**
	 * 转set
	 */
	public static void toSet() {
		Set<User> collect = list.stream().collect(Collectors.toSet());
		Iterator<User> iterator = collect.iterator();
		while(iterator.hasNext()) {
			System.out.println(iterator.next().getUserId());
		}
	}

	/**
	 * 转map
	 */
	public static void toMap() {
		Map<Integer, User> collect = list.stream().collect(Collectors.toMap(User::getUserId, u -> u));
		for (Integer in : collect.keySet()) {
		  User u = collect.get(in);//得到每个key多对用value的值
		  println(u);
		}
	}
	/**
	 *map
	 */
	public static void map() {
		list.stream().map(User::getUserId).forEach(userId -> println(userId));
		list.stream().mapToInt(User::getAge).forEach(userId -> println(userId));
		list.stream().mapToDouble(User::getUserId).forEach(userId -> println(userId));
		list.stream().mapToLong(User::getUserId).forEach(userId -> println(userId));
	}
	
	/**
	 * 查找与匹配
	 * allMatch方法与anyMatch差不多,表示所有的元素都满足才返回true。noneMatch方法表示没有元素满足
	 */
	public static void anyMatch() {
		boolean anyMatch = list.stream().anyMatch(u -> u.getAge() == 100);
		boolean allMatch = list.stream().allMatch(u -> u.getUserId() == 10);
		boolean noneMatch = list.stream().noneMatch(u -> u.getUserId() == 10);
		println(anyMatch);
		println(allMatch);
		println(noneMatch);
	}
	
	/**
	 * reduce操作
	 */
	public static void reduce() {
		Optional<Integer> sum = list.stream().map(User::getAge).reduce(Integer::sum);
		Optional<Integer> max = list.stream().map(User::getAge).reduce(Integer::max);
		Optional<Integer> min = list.stream().map(User::getAge).reduce(Integer::min);
		println(sum);
		println(max);
		println(min);
	}
	/**
	 * 公共输出
	 * @param c
	 */
	public static void println(Object c) {
		System.out.println(c.toString());
	}
	

	static class User {
		private Integer userId;
		
		private String name;
		
		private Integer age;
		
		User(Integer userId, String name, Integer age) {
			super();
			this.userId = userId;
			this.name = name;
			this.age = age;
		}
		
		public Integer getUserId() {
			return userId;
		}

		public void setUserId(Integer userId) {
			this.userId = userId;
		}

		public String getName() {
			return this.name;
		}

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

		public Integer getAge() {
			return age;
		}

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

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

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