Java学习打卡Day36

知识总结

Stream API

用的情况下能够简化那些操作
它是以个接口，它有一个泛型
集合和流，集合是用来管理和使用的
流是做什么，不管怎么做

1. Stream是Java8中处理数组、集合的抽象概念
   可以执行非常复杂的查找、过滤、映射等操作。
   Stream.出的东西叫做中间操作。
2. 常用方法（中间操作）
   Stream filter(Predicate) predicate); 过滤
   Stream limit(long maxSize);截断，不超过给定的数量
   Stream distinct(); 筛选，利用hashCode和equals
   Stream map(Function mapper);
   Stream sorted();自然排序
   Stream sorted(Comparator comparator);定制排序
3. 常用方法（终止操作）
   Long count();返回流中的总个数
   Void forEach(Consumer action);遍历
   Boolean anyMatch(Predicate predicate);是否至少匹配一个
   Boolean allMath(Predicate predicate);是否匹配所有元素
   Boolean noneMatch(Predicate predicate);是否没有匹配
   Optional findFirst();返回第一个
   OptionalfindAny();返回任意
   Optionalmin(Comparatorcomparator);返回最小
   Optionalmax(Comparator comparator);返回最大

案例

package com.wx.day36.t1.stream;

import java.util.*;
import java.util.function.Consumer;
import java.util.stream.Stream;

public class TestCreateStream {

	public static void main(String[] args) {
		//Stream--->集合、数组
		List<String> list = new ArrayList<String>();
		
		list.add("zhangsan");
		list.add("lisi");
		list.add("wangwu");
		list.add("zhaoliu");
		list.add("zhangsan");
		
		//做什么，而不是怎么做
		//Stream里存的是数据的操作，自身不保存数据
		//1.创建Stream
		Stream<String> stream = list.stream();
		//2.中间操作
		Stream<String> center =  stream.filter((s)->s.length() >= 5);
		//3.终止操作 最终操作
		System.out.println("名字长度大于5的是：");
		center.forEach(System.out::println);
		
		//简化
		list.stream().filter((s)->s.length()>=5).forEach(System.out::println);
		
		
		List<String> newList = new ArrayList<String>();
		for(String s:list){
			if(s.length()>=5)
				newList.add(s);	
		}
		System.out.println("名字长度大于等于5的是:");
		for(String s: newList)
			System.out.println(s);
	}
}

package com.wx.day36.t1.stream;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class TestStreamMethod {

	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();

		list.add("zhangsan");
		list.add("lisi");
		list.add("wangwu");
		list.add("zhaoliu");
		list.add("zhangsan");
		
		System.out.println("------------filter----------");
		//filter--->过滤 指定规则
		list.stream().filter((s)->s.startsWith("z")).filter((s)->s.contains("s")).forEach(System.out::println);
		System.out.println("--------------limit---------------");
		//limit--->截断，返回不超过指定数量
		list.stream().limit(4).forEach(System.out::println);
		System.out.println("-----------------------------");
		//distinct--->筛选,利用hashcode和equals
		list.stream().distinct().forEach(System.out::println);
		
		System.out.println("-----------distinct------------");
		List<Emp> elist = new ArrayList<>();
		elist.add(new Emp("高强", 28, 10));
		elist.add(new Emp("高蓝轩", 28, 10));
		elist.add(new Emp("高f强", 78, 100));
		elist.add(new Emp("高f强", 78, 100));
		elist.add(new Emp("高强", 28, 10));
		//不会影响元数据
		elist.stream().distinct().forEach(System.out::println);
		System.out.println("-----------------------------");
		elist.forEach(System.out::println);
		
		//map值得是 不是集合
		System.out.println("--------------Map------------");
		//emp-->T   getName()-->R
		elist.stream().map((emp)->emp.getName()).forEach(System.out::println);
		elist.stream().map((emp)->emp.getScore()).forEach(System.out::println);
	
		List<String> strlist = Arrays.asList("aaa","bbb","ccc","dddf");
		strlist.stream().map((s)->s.toUpperCase()).forEach(System.out::println);
		System.out.println("-----------------------------");
		strlist.stream().map(String::toUpperCase).forEach(System.out::println);
		
		//sorted排序,流中的元素实现Comparable接口
		list.stream().sorted().forEach(System.out::println);
		System.out.println("--------------sorted(Comparator)---------------");
		elist.stream().sorted((x,y)->Double.compare(x.getScore(), y.getScore())).forEach(System.out::println);
	}

}

package com.wx.day36.t1.stream;

public class Emp {
	private String name;
	private int age;
	private double score;
	
	public int hashCode(){
		return (int)(this.name.hashCode() + this.age + this.score);
	}
	public boolean equals(Object obj){
		//1.比较两个引用是否指向同一个对象
		if(this==obj)
			return true;
		//2.obj是否为空
		if(obj==null)
			return false;
		//3.判断两个引用的实际类型
		if(this.getClass()!=obj.getClass())
			return false;
		//4.强转
		Emp emp = (Emp)obj;
		//5.比较
		if(this.name.equals(emp.getName()) && this.age == emp.getAge() && this.score==emp.getScore())
			return true;
		return false;
	}
	public Emp(){
		super();
	}
	public Emp(String name, int age, double score) {
		super();
		this.name = name;
		this.age = age;
		this.score = score;
	}
	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 getScore() {
		return score;
	}
	public void setScore(double score) {
		this.score = score;
	}
	@Override
	public String toString() {
		return "Emp [name=" + name + ", age=" + age + ", score=" + score + "]";
	}
	
}

package com.wx.day36.t2.end;

import java.util.ArrayList;
import java.util.List;

public class TestEndMethod {

	public static void main(String[] args) {
		
		List <String> list = new ArrayList<String>();
		list.add("Blsit");
		list.add("dlsit");
		list.add("fglsit");
		list.add("hsit");
		list.add("sdfgit");
		list.add("sdfgfdsit");
		list.add("hhhsit");
		
		int count = (int)list.stream().filter((s)->s.length()>=3).count();
		System.out.println(count);
		
		boolean b1 = list.stream().filter((s)->s.length()>=5).anyMatch((s)->s.startsWith("f"));
		System.out.println(b1);
	
		boolean b2 = list.stream().filter((s)->s.length()>=6).allMatch((s)->s.contains("t"));
		System.out.println(b2);
	
		boolean b3 = list.stream().filter((s)->s.length()>=7).noneMatch((s)->s.contains("t"));
		System.out.println(b3);
	
		String str = list.stream().filter((s)->s.length()>=5).findFirst().get();
		System.out.println(str);
	
		String str2 = list.stream().filter((s)->s.length()>=6).findAny().get();
		System.out.println(str2);
	
		
	}

}

package com.wx.day36.t3.threads;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

public class TestStream {

	public static void main(String[] args) {
		List <String> list = new  ArrayList<String>();
		for(int i = 0 ; i < 306600 ; i++){
			UUID u = UUID.randomUUID();
			list.add(u.toString());
		}
//		long start = System.currentTimeMillis();
//		long count = list.stream().sorted().count();
//		System.out.println(count);
//		long end = System.currentTimeMillis();
//		System.out.println(end-start);
//		
		long start = System.currentTimeMillis();
		long count = list.parallelStream().sorted().count();
		System.out.println(count);
		long end = System.currentTimeMillis();
		System.out.println(end-start);
	}

}