一、流 转换为数组、集合package com.java.design.java8.Stream;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.ArrayList;import java.util.List;import java.util.stream.Stream;/** * @author 陈杨 /@SpringBootTest@RunWith(SpringRunner.class)public class ListChange { private Stream<String> stream = Stream.of(“Kirito”, “Asuna”, “Illyasviel”, “Sakura”); @Test public void testListChange() { // 将流转换为数组 // System.out.println("————-将流转换为数组—————"); // String[] array = stream.toArray(len -> new String[len]); // String[] array = stream.toArray(String[]::new); // Arrays.asList(array).stream().forEach(System.out::println); // 将流转换为集合 // System.out.println("————-将流转换为集合—————"); // System.out.println("——-Collectors.toList()解析———–"); / public static <T> * Collector<T, ?, List<T>> toList() { * return new CollectorImpl<>((Supplier<List<T>>) ArrayList::new, List::add, * (left, right) -> { left.addAll(right); return left; }, * CH_ID); }/ // List<String> list = stream.collect(Collectors.toList()); // List<String> linkedList = stream.collect(LinkedList::new,LinkedList::add,LinkedList::addAll); List<String> list = stream.collect(ArrayList::new, ArrayList::add, ArrayList::addAll); list.forEach(System.out::println); System.out.println(list.getClass()); // System.out.println("——-Collectors.toCollection()解析—–"); / public static <T, C extends Collection<T>> * Collector<T, ?, C> toCollection(Supplier<C> collectionFactory) { * return new CollectorImpl<>(collectionFactory, Collection<T>::add, * (r1, r2) -> { r1.addAll(r2); return r1; }, * CH_ID); }*/ // List<String> list =stream.collect(Collectors.toCollection(ArrayList::new)); // List<String> linkedList =stream.collect(Collectors.toCollection(ArrayList::new)); // Set<String> treeSet =stream.collect(Collectors.toCollection(TreeSet::new)); // Set<String> hashSet =stream.collect(Collectors.toCollection(HashSet::new)); }} . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.1.2.RELEASE)2019-02-20 15:47:22.310 INFO 1348 --- [ main] com.java.design.java8.Stream.ListChange : Starting ListChange on DESKTOP-87RMBG4 with PID 1348 (started by 46250 in E:\IdeaProjects\design)2019-02-20 15:47:22.311 INFO 1348 --- [ main] com.java.design.java8.Stream.ListChange : No active profile set, falling back to default profiles: default2019-02-20 15:47:22.947 INFO 1348 --- [ main] com.java.design.java8.Stream.ListChange : Started ListChange in 0.914 seconds (JVM running for 1.774)KiritoAsunaIllyasvielSakuraclass java.util.ArrayList二、集合排序package com.java.design.java8.Stream;import org.junit.Before;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.*;/** * @author 陈杨 */@SpringBootTest@RunWith(SpringRunner.class)public class ComparatorDetail { private List<String> names; @Before public void init() { names = Arrays.asList("Kirito", "Asuna", "Sinon", "Yuuki", "Alice"); } public void println() { System.out.println(names); System.out.println("-----------------------------------------\n"); } @Test public void testComparatorDetail() { // 对名字进行升序排序 Collections.sort(names); this.println(); // 对名字进行降序排序 names.sort(Collections.reverseOrder()); this.println(); // 按照姓名的字符串长度升序排序 相同长度-->比较前两个字符-->按照字符的ASCII码大小升序排序 names.sort(Comparator.comparingInt(String::length) .thenComparing(str -> str.charAt(0)) .thenComparing(str -> str.charAt(1)) ); this.println(); // 按照姓名的字符串长度降序排序 相同长度-->比较前两个字符-->按照字符的ASCII码大小降序排序 names.sort(Comparator.comparingInt(String::length) .thenComparing(str -> str.charAt(0)) .thenComparing(str -> str.charAt(1)) .reversed()); this.println(); // 按照姓名的字符串长度降序排序 相同长度-->按照字符的ASCII码大小排序(不区分大小写) names.sort(Comparator.comparingInt(String::length) .thenComparing(String.CASE_INSENSITIVE_ORDER)); this.println(); }} . ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _ | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: Spring Boot :: (v2.1.2.RELEASE)2019-02-20 15:58:39.959 INFO 4588 — [ main] c.j.d.java8.Stream.ComparatorDetail : Starting ComparatorDetail on DESKTOP-87RMBG4 with PID 4588 (started by 46250 in E:\IdeaProjects\design)2019-02-20 15:58:39.962 INFO 4588 — [ main] c.j.d.java8.Stream.ComparatorDetail : No active profile set, falling back to default profiles: default2019-02-20 15:58:40.459 INFO 4588 — [ main] c.j.d.java8.Stream.ComparatorDetail : Started ComparatorDetail in 0.729 seconds (JVM running for 1.462)[Alice, Asuna, Kirito, Sinon, Yuuki]—————————————–[Yuuki, Sinon, Kirito, Asuna, Alice]—————————————–[Alice, Asuna, Sinon, Yuuki, Kirito]—————————————–[Kirito, Yuuki, Sinon, Asuna, Alice]—————————————–[Alice, Asuna, Sinon, Yuuki, Kirito]—————————————–三、Stream之map(Lambda)package com.java.design.java8.Stream;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.Arrays;import java.util.Collections;import java.util.List;import java.util.stream.Collectors;/** * @author 陈杨 /@SpringBootTest@RunWith(SpringRunner.class)public class StringOperation { private List<String> list = Arrays.asList(“Kirito”, “Asuna”, “Illyasviel”, “Sakura”); private List<List<String>> listMap = Arrays.asList(Collections.singletonList(“Kirito”), Collections.singletonList(“Asuna”), Collections.singletonList(“Illyasviel”), Collections.singletonList(“Sakura”)); private List<List<String>> listFlatMap = Arrays.asList(Collections.singletonList(“Kirito”), Collections.singletonList(“Asuna”), Collections.singletonList(“Illyasviel”), Collections.singletonList(“Sakura”)); @Test public void testStringOperation() { // 集合中 每个字符串 按照排列先后顺序拼接 形成一个长字符串 // String concat = // list.stream().collect(StringBuilder::new, StringBuilder::append, StringBuilder::append).toString(); // String concat = list.stream().collect(Collectors.joining()); // System.out.println(concat); // 集合中 对每个字符串元素 将所有字母变成大写字母 System.out.println("—————————————–\n"); List<String> upperCase = list.stream().map(String::toUpperCase).collect(Collectors.toList()); upperCase.forEach(System.out::println); // 集合中 对每个字符串元素 将所有字母变成小写字母 System.out.println("—————————————–\n"); List<String> lowerCase = list.stream().map(String::toLowerCase).collect(Collectors.toList()); lowerCase.forEach(System.out::println); System.out.println("—————————————–\n"); System.out.println(“FlatMap与Map的区别:\n”); // map: 对多个list 分别map Fuction 映射 形成多个list System.out.println("—————————————–\n"); System.out.println(“进行map映射:”); List<List<String>> upperMap = listMap.stream() .map(list -> list.stream().map(String::toUpperCase) .collect(Collectors.toList())).collect(Collectors.toList()); upperMap.forEach(System.out::println); // FlatMap： 对多个list 进行flat扁平化 后再进行map Fuction 映射 形成一个list System.out.println("—————————————–\n"); System.out.println(“FlatMap扁平化进行map映射:”); List<String> upperFlatMap = listFlatMap.stream() .flatMap(list -> list.stream().map(String::toUpperCase)).collect(Collectors.toList()); upperFlatMap.forEach(System.out::println); }} . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.1.2.RELEASE)2019-02-20 15:50:07.423 INFO 8208 --- [ main] c.j.design.java8.Stream.StringOperation : Starting StringOperation on DESKTOP-87RMBG4 with PID 8208 (started by 46250 in E:\IdeaProjects\design)2019-02-20 15:50:07.424 INFO 8208 --- [ main] c.j.design.java8.Stream.StringOperation : No active profile set, falling back to default profiles: default2019-02-20 15:50:07.917 INFO 8208 --- [ main] c.j.design.java8.Stream.StringOperation : Started StringOperation in 0.717 seconds (JVM running for 1.5)-----------------------------------------KIRITOASUNAILLYASVIELSAKURA-----------------------------------------kiritoasunaillyasvielsakura-----------------------------------------FlatMap与Map的区别:-----------------------------------------进行map映射:[KIRITO][ASUNA][ILLYASVIEL][SAKURA]-----------------------------------------FlatMap扁平化进行map映射:KIRITOASUNAILLYASVIELSAKURA四、内部迭代与外部迭代package com.java.design.java8.Stream;import com.java.design.java8.entity.Student;import com.java.design.java8.entity.Students;import org.junit.Before;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.*;/** * @author 陈杨 */@SpringBootTest@RunWith(SpringRunner.class)//迭代本质public class IterativeEssence { private List<Student> students; @Before public void init() { students = new Students().init(); } @Test public void testIterativeEssence() { // 需求： select name from students where age > 14 and addr ="Sword Art Online" order by id desc ; // 外部迭代 System.out.println("-----------------------------------------\n"); System.out.println("外部迭代"); List<Student> list = new ArrayList<>(); for (Student student : students) { if (student.getAge() > 14 && student.getAddr().equals("Sword Art Online")) { list.add(student); } } list.sort(Comparator.comparingInt(Student::getId)); for (Student student : list) { System.out.println(student.getName()); } // 内部迭代 System.out.println("-----------------------------------------\n"); System.out.println("内部迭代"); students.stream() .filter(student -> student.getAge() > 14) .filter(student -> student.getAddr().equals("Sword Art Online")) .sorted(Comparator.comparingInt(Student::getId)). forEach(student -> System.out.println(student.getName())); // 备注： // 内部迭代与SQL语句属于描述性语言 // 集合关注的是数据与数据存储 // 流关注的是数据的计算 // 流中间操作返回的都是Stream对象 泛型取决于中间操作的类型 // 流终止操作： 无返回值（forEach） 返回值是其他类型 }} . ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _ | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: Spring Boot :: (v2.1.2.RELEASE)2019-02-20 15:53:03.633 INFO 8864 — [ main] c.j.d.java8.Stream.IterativeEssence : Starting IterativeEssence on DESKTOP-87RMBG4 with PID 8864 (started by 46250 in E:\IdeaProjects\design)2019-02-20 15:53:03.640 INFO 8864 — [ main] c.j.d.java8.Stream.IterativeEssence : No active profile set, falling back to default profiles: default2019-02-20 15:53:04.167 INFO 8864 — [ main] c.j.d.java8.Stream.IterativeEssence : Started IterativeEssence in 0.746 seconds (JVM running for 1.455)—————————————–外部迭代KiritoAsuna—————————————–内部迭代KiritoAsuna五、串行流与并行流 简单性能测试package com.java.design.java8.Stream;import org.junit.Before;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.ArrayList;import java.util.Arrays;import java.util.List;import java.util.UUID;import java.util.concurrent.TimeUnit;import java.util.function.Function;import java.util.stream.Collectors;import java.util.stream.IntStream;/* * @author 陈杨 /@RunWith(SpringRunner.class)@SpringBootTestpublic class ErgodicString { private List<String> uuid; private long startTime; private long endTime; private long parallelEndTime; @Before public void init() { uuid = new ArrayList<>(10000000); IntStream.range(0, 10000000).forEach(i -> uuid.add(UUID.randomUUID().toString())); } public void testNormal() { startTime = System.nanoTime(); uuid.stream().sorted().collect(Collectors.toList()); endTime = System.nanoTime(); long millis = TimeUnit.NANOSECONDS.toMillis(endTime - startTime); System.out.println(“单线程” + millis); } public void testParallel() { startTime = System.nanoTime(); uuid.parallelStream().sorted().collect(Collectors.toList()); parallelEndTime = System.nanoTime(); long millis = TimeUnit.NANOSECONDS.toMillis(parallelEndTime - startTime); System.out.println(“多线程” + millis); } @Test public void testErgodicString() { List<String> list = Arrays.asList(“Kirito”, “Asuna”, “Illyasviel”, “Sakura”); // 需求： 将数组中每个元素各个字母大写 并放入集合 System.out.println("——————–串行流stream———————"); // spliterator 分割迭代器 // 串行流stream() 单线程处理 / * default Stream<E> stream() { * return StreamSupport.stream(spliterator(), false);} / // List<String> collect = list.stream().map(str -> str.toUpperCase()).collect(Collectors.toList()); // R apply(T t); toUpperCase() 没有参数作为输入 // 但把调用toUpperCase的对象作为T作为输入 返回的R是return的对象结果 // List<String> collect = list.stream().map(String::toUpperCase).collect(Collectors.toList()); Function<String, String> function = String::toUpperCase; //等价于 (String str) -> str.toUpperCase() //方法引用 类的类型::实例方法 对应的lambda表达式 第一个输入参数 是调用此方法的对象 List<String> collect = list.stream().map(function).collect(Collectors.toList()); collect.forEach(System.out::println); this.testNormal(); System.out.println("—————–并行流parallelStream——————"); // 并行流parallelStream() 多线程处理 / * default Stream<E> parallelStream() { * return StreamSupport.stream(spliterator(), true);} */ List<String> parallelCollect = list.parallelStream().map(str -> str.toUpperCase()).collect(Collectors.toList()); parallelCollect.forEach(System.out::println); this.testParallel(); }} . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / ` | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: Spring Boot :: (v2.1.2.RELEASE)2019-02-20 15:54:54.321 INFO 7356 — [ main] c.j.design.java8.Stream.ErgodicString : Starting ErgodicString on DESKTOP-87RMBG4 with PID 7356 (started by 46250 in E:\IdeaProjects\design)2019-02-20 15:54:54.323 INFO 7356 — [ main] c.j.design.java8.Stream.ErgodicString : No active profile set, falling back to default profiles: default2019-02-20 15:54:54.817 INFO 7356 — [ main] c.j.design.java8.Stream.ErgodicString : Started ErgodicString in 0.705 seconds (JVM running for 1.528)——————–串行流stream———————KIRITOASUNAILLYASVIELSAKURA单线程10590—————–并行流parallelStream——————KIRITOASUNAILLYASVIELSAKURA多线程3313
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