Java1.8中的Collections类的功能增强很多，你可以直接调用串行的Collections.stream()或并行的Collections.parallelStream()来对List，Set中的数据进行处理与操作（不支持Map）。

1：stream是什么？

    java.util.Stream是一个接口,是1.8引入。它表示了某原子的序列，可以对原子进行各种操作，Stream可以是中间操作，也可以做为最重操作。作为中间操作时返回流对象本身，作为最重操作时返回某种类型的值。作为中间操作时可以在这个流上多次调用操作方法。

2：lambda表达式

其实lambda表达式实质上是个匿名函数，它由三部分组成：参数列表，箭头（->），以及一个表达式或语句块。来看一个示例：

public void sum(int a, int b){    return a+b;}

转为 lambda表达式为

(int a, int b) -> a + b;

还可以这样写，因为java会根据上下文推断出参数类型

(a, b) -> {return a + b;}

或

(a, b) -> a + b;

3：具体示例

package cn.huiyunche.driver.controller;import java.util.ArrayList;import java.util.List;import java.util.UUID;import java.util.concurrent.TimeUnit;import java.util.stream.Collectors;import org.apache.commons.collections.CollectionUtils;public class Lambda {	private static List
    
      lambdaList = new ArrayList<>();		private static String string = "string";	private static String integer = "integer";		public Lambda() {		initData(string);	}		public static void initData(String flag) {		if (CollectionUtils.isNotEmpty(lambdaList)) {			lambdaList.clear();		}		if (string.equals(flag)) {			lambdaList.add("Ulrica");			lambdaList.add("Quella");			lambdaList.add("Cecilia");			lambdaList.add("Claudia");			lambdaList.add("Desdemona");			lambdaList.add("Indira");		} else {			lambdaList.add("1");			lambdaList.add("2");			lambdaList.add("2");			lambdaList.add("3");			lambdaList.add("3");			lambdaList.add("4");			lambdaList.add("4");			lambdaList.add("4");			lambdaList.add("5");			lambdaList.add("5");			lambdaList.add("5");			lambdaList.add("6");			lambdaList.add("6");		}	}		// 这种方式就不多讲了，以前旧版本比较常见的做法	public static void runThreadUseInnerClass() {        new Thread(new Runnable() {            @Override            public void run() {                System.out.println("内部类实现的线程");            }        }).start();    }		// 新版本写法	public static void thred() {		new Thread(() -> System.out.println("内部类实现的线程")).start();	}		// 遍历list	public static void ergodicList() {		initData(string);		System.out.println("=================遍历list开始==========>>>>>>>>>>>");		lambdaList.forEach((value) -> System.out.println("value = " + value));		System.out.println("<<<<<<<<<<<======遍历list结束=====================");	}		// 正序排序list	public static void asc() {		initData(integer);		System.out.println("=================正序排序list开始==========>>>>>>>>>>>");		lambdaList.stream().sorted().forEach((value) -> System.out.println("value = " + value));		System.out.println("=================正序排序list结束==========>>>>>>>>>>>");	}		// 倒序排序list	public static void desc() {		initData(integer);		System.out.println("=================倒序排序list开始==========>>>>>>>>>>>");		lambdaList.stream().sorted((a, b) -> b.compareTo(a)).forEach((value) -> System.out.println("value = " + value));		System.out.println("=================倒序排序list结束==========>>>>>>>>>>>");	}		// 过滤	public static void filter(String val) {		initData(string);		System.out.println("=================过滤开始==========>>>>>>>>>>>");		lambdaList.stream().filter((value) -> value.toLowerCase().contains(val.toLowerCase())).forEach((value) -> System.out.println("value = " + value));		System.out.println("=================过滤结束==========>>>>>>>>>>>");	}		// map使用	public static void map() {		initData(string);		System.out.println("=================map使用开始==========>>>>>>>>>>>");		//lambdaList.stream().map((value) -> value.toUpperCase()).forEach((value) -> System.out.println("value = " + value));		lambdaList.stream().map(String::toUpperCase).forEach((value) -> System.out.println("value = " + value));		System.out.println("=================map使用结束==========>>>>>>>>>>>");	}		//parallelStream (并行) 和 stream（串行）	public static void stream() {		System.out.println("=================parallelStream (并行) 和 stream（串行）开始==========>>>>>>>>>>>");		int max = 1000000;		long t0, t1, count, millis;		List
     
       list = new ArrayList<>(max);		for (int i = 0; i < max; i++) {			UUID uuid = UUID.randomUUID();			list.add(uuid.toString());		}		// 串行		t0 = System.nanoTime();		count = list.stream().sorted().count();		System.out.println("count = " + count);		t1 = System.nanoTime();		millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);		System.out.println(String.format("串行排序耗时: %d ms", millis));				System.out.println("===========================");				long t00, t11, count0, millis0;		List
      
        list0 = new ArrayList<>(max);		for (int i = 0; i < max; i++) {			UUID uuid = UUID.randomUUID();			list0.add(uuid.toString());		}		// 串行		t00 = System.nanoTime();		count0 = list0.stream().sorted().count();		System.out.println("count0 = " + count0);		t11 = System.nanoTime();		millis0 = TimeUnit.NANOSECONDS.toMillis(t11 - t00);		System.out.println(String.format("并行排序耗时: %d ms", millis0));				System.out.println("===========================");				long millis00;		millis00 = TimeUnit.NANOSECONDS.toMillis((t1 - t0) - (t11 - t00));		System.out.println(String.format("串行比并行排序多耗时: %d ms", millis00));				System.out.println("=================parallelStream (并行) 和 stream（串行）结束==========>>>>>>>>>>>");	}		// noneMatch	public static void noneMatch(String val) {		System.out.println("=================noneMatch使用开始==========>>>>>>>>>>>");		initData(string);		boolean bool = lambdaList.stream().noneMatch((value) -> value.contains(val));		System.out.println("contains bool = " + bool);		bool = lambdaList.stream().noneMatch((value) -> value.endsWith(val));		System.out.println("endsWith bool = " + bool);		bool = lambdaList.stream().noneMatch((value) -> value.startsWith(val));		System.out.println("startsWith bool = " + bool);		System.out.println("=================noneMatch使用结束==========>>>>>>>>>>>");			}		// allMatch	public static void allMatch(String val) {		System.out.println("=================allMatch使用开始==========>>>>>>>>>>>");		initData(string);		boolean bool = lambdaList.stream().allMatch((value) -> value.startsWith(val));		System.out.println("bool = " + bool);		System.out.println("=================allMatch使用结束==========>>>>>>>>>>>");			}		// anyMatch	public static void anyMatch(String val) {		System.out.println("=================anyMatch使用开始==========>>>>>>>>>>>");		initData(string);		boolean bool = lambdaList.stream().anyMatch((value) -> value.matches(val));		System.out.println("bool = " + bool);		System.out.println("=================anyMatch使用结束==========>>>>>>>>>>>");			}		// collect(过滤数据，返回List)	public static void collect(String val) {		System.out.println("=================collect使用开始==========>>>>>>>>>>>");		initData(string);		List
       
         lists = lambdaList.stream().filter((value) -> value.toLowerCase().contains(val.toLowerCase())).collect(Collectors.toList());		System.out.println(String.format("lists.size: %d ", lists.size()));		lists.forEach((value) -> System.out.println("value = " + value));		System.out.println("=================collect使用结束==========>>>>>>>>>>>");			}		// reduce(拼接数据只返回一个结果集)	public static void reduce() {		System.out.println("=================reduce使用开始==========>>>>>>>>>>>");		initData(string);		lambdaList.stream().reduce((value1, value2) -> value1 + value2).ifPresent(System.out::println);		System.out.println("=================reduce使用结束==========>>>>>>>>>>>");			}		// 统计大于2小于5	public static void groupBysum() {		System.out.println("=================统计大于2小于5使用开始==========>>>>>>>>>>>");		initData(integer);		lambdaList.parallelStream().map(Integer::new).filter(val -> val >= 2 && val <= 6).collect(Collectors.groupingBy(p -> new Integer(p), Collectors.summingInt(p -> p))).forEach((key, value) -> System.out.println("key = " + key + " value = " +value));		System.out.println("=================统计大于2小于5使用结束==========>>>>>>>>>>>");	}		public static void main(String[] args) {		thred();		runThreadUseInnerClass();		ergodicList();		asc();		desc();		filter("c");		map();		stream();		noneMatch("Claudia");		allMatch("U");		anyMatch("Claudia");		collect("c");		reduce();		groupBysum();	}}
       
      
     
    

输出结果

内部类实现的线程内部类实现的线程=================遍历list开始==========>>>>>>>>>>>value = Ulricavalue = Quellavalue = Ceciliavalue = Claudiavalue = Desdemonavalue = Indira<<<<<<<<<<<======遍历list结束======================================正序排序list开始==========>>>>>>>>>>>value = 1value = 2value = 3value = 4value = 4value = 4value = 5value = 6=================正序排序list结束==========>>>>>>>>>>>=================倒序排序list开始==========>>>>>>>>>>>value = 6value = 6value = 5value = 4value = 3value = 2value = 1=================倒序排序list结束==========>>>>>>>>>>>=================过滤开始==========>>>>>>>>>>>value = Ulricavalue = Ceciliavalue = Claudia=================过滤结束==========>>>>>>>>>>>=================map使用开始==========>>>>>>>>>>>value = ULRICAvalue = QUELLAvalue = CECILIAvalue = CLAUDIAvalue = DESDEMONAvalue = INDIRA=================map使用结束==========>>>>>>>>>>>=================parallelStream (并行) 和 stream（串行）开始==========>>>>>>>>>>>count = 1000000串行排序耗时: 826 ms===========================count0 = 1000000并行排序耗时: 781 ms===========================串行比并行排序多耗时: 44 ms=================parallelStream (并行) 和 stream（串行）结束==========>>>>>>>>>>>=================noneMatch使用开始==========>>>>>>>>>>>contains bool = falseendsWith bool = falsestartsWith bool = false=================noneMatch使用结束==========>>>>>>>>>>>=================allMatch使用开始==========>>>>>>>>>>>bool = false=================allMatch使用结束==========>>>>>>>>>>>=================anyMatch使用开始==========>>>>>>>>>>>bool = true=================anyMatch使用结束==========>>>>>>>>>>>=================collect使用开始==========>>>>>>>>>>>lists.size: 3 value = Ulricavalue = Ceciliavalue = Claudia=================collect使用结束==========>>>>>>>>>>>=================reduce使用开始==========>>>>>>>>>>>UlricaQuellaCeciliaClaudiaDesdemonaIndira=================reduce使用结束==========>>>>>>>>>>>=================统计大于2小于5使用开始==========>>>>>>>>>>>key = 2 value = 4key = 3 value = 6key = 4 value = 12key = 5 value = 15key = 6 value = 12=================统计大于2小于5使用结束==========>>>>>>>>>>>