public class Test10 {
static List numbers = Arrays.asList(1, 5, 3, 2, 4);
static List strs = Arrays.asList("b2", "b1", "a2", "c", "b", "a");
static List> strsList = Arrays.asList(strs);
static Person p1 = new Person(GenderEnum.MALE, 20, "Jack");
static Person p2 = new Person(GenderEnum.FEMALE, 20, "Lily");
static Person p3 = new Person(GenderEnum.MALE, 10, "John");
static Person p4 = new Person(GenderEnum.FEMALE, 10, "Lucy");
static Person p5 = new Person(GenderEnum.MALE, 20, "Eason");
static List persons = Arrays.asList(p1, p2, p3, p4, p5);
static void method1() {
// 常用数据结构转流的方式
// Collection接口 提供了stream()方法
// 1. List转流
List list = new ArrayList<>();
Stream streamA = list.stream();
// ------------------------------------------------------------
// 2. Set转流
Set set = new HashSet<>();
Stream streamB = set.stream();
// ------------------------------------------------------------
// 3. Map转流
Map map = new HashMap<>();
Stream> streamC = map.entrySet().stream();
Stream streamD = map.values().stream();
// ------------------------------------------------------------
// 4. 数组转流
String[] arr = { "A", "B", "C" };
Arrays.stream(arr);
// ------------------------------------------------------------
// 5. Iterable转流
Iterable iterable = new ArrayList<>();
StreamSupport.stream(iterable.spliterator(), false);
}
static void method2() {
// 流的拼接
List listA = Arrays.asList("s1", "s2", "s3");
List listB = Arrays.asList("t1", "t2", "t3");
// Stream.concat()实现多个流拼接
Stream streamA = Stream.concat(listA.stream(), listB.stream());
// Stream.of()实现拼接
// 多个元素
Stream streamB = Stream.of("A", "B", "C");
// 多个List
Stream streamC = Stream.of(listA, listB).flatMap(Collection::stream);
// 多个Stream
Stream streamD = Stream.of(listA.stream(), listB.stream()).flatMap(Function.identity());
// flatMap实现子元素拼接
List- items = new ArrayList<>();
Stream streamE = items.stream().flatMap(i -> i.getSubItems().stream());
}
static void method3() {
// 高级收集器
// 1. 字符串拼接
List strs = Arrays.asList("s1", "s2", "s3");
// 无分隔符
String str1 = strs.stream().collect(Collectors.joining());
// 单个分隔符
String str2 = strs.stream().collect(Collectors.joining(","));
// 前后缀及分隔符
String str3 = strs.stream().collect(Collectors.joining(",", "[", "]"));
// ----------------------------------------------------------------------------------------------------
// 返回集合
// 2. 返回数组
// Object数据（无参默认）
Object[] arr1 = strs.stream().toArray();
// 特定类型数据
String[] arr2 = strs.stream().toArray(String[]::new);
// 数组指定长度
String ids = "1, 2, 3, 4";
String[] arr3 = Arrays.asList(ids.split(",")).stream().map(String::trim).toArray(size -> new String[size]);
// ----------------------------------------------------------------------------------------------------
// 3. 返回List
// 默认List
List list1 = strs.stream().filter(str -> str.length() > 5).map(String::toUpperCase).collect(Collectors.toList());
// 返回特定类型如ArrayList
List list2 = strs.stream().filter(str -> str.length() > 5).map(String::toUpperCase).collect(Collectors.toCollection(ArrayList::new));
// ----------------------------------------------------------------------------------------------------
// 4. 返回Map
// List转Map
List
- items = Arrays.asList(new Item("0001", "name"), new Item("0002", "name2"));
// 成员作为value
Map map1 = items.stream().collect(Collectors.toMap(Item::getItemId, Item::getName));
// 元素作为value
Map map2 = items.stream().collect(Collectors.toMap(Item::getItemId, Function.identity()));
// value重复取第一个
Map map3 = items.stream().collect(Collectors.toMap(Item::getItemId, Function.identity(), (n1, n2) -> n1));
// value重复自定义异常，指定返回类型
Map map4 = items.stream()
.collect(Collectors.toMap(Item::getItemId, Function.identity(), (a, b) -> {
throw new IllegalStateException("cannot add duplicate key: " + a);
}, IdentityHashMap::new));
// Map转Map
Map map = new HashMap<>();
Map map_ = map.entrySet().stream().filter(e -> e.getValue() > 10).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
}
static void method4() {
// 排序 sorted
// 数字排序
List numbers = Arrays.asList(1, 5, 3, 2, 4);
// 1. 升序(默认）
numbers.stream().sorted();
// 1, 2, 3, 4, 5
// 2. 降序
numbers.stream().sorted(Comparator.reverseOrder());
// 5, 4, 3, 2, 1
// --------------------------------------------------------------------------------
// 字符排序
List strs = Arrays.asList("b2", "b1", "a2", "c", "b", "a");
// 1. 默认
List strSorted1 = strs.stream().sorted().collect(Collectors.toList());
// a, a2, b, b1, b2, c
// 2. 自定义：先比较长度
strs.stream().sorted((s1, s2) -> s1.length() - s2.length());
List strSorted2 = strs.stream()
.sorted(Comparator.comparing(String::length).thenComparing(Comparator.naturalOrder()))
.collect(Collectors.toList());
// a, b, c, a2, b1, b2
// --------------------------------------------------------------------------------
// 自定义类型排序
// 1. 可实现Comparable接口
List pVal = persons.stream().sorted().collect(Collectors.toList());
/*
* Person [gender=MALE, age=10, name=John]
* Person [gender=MALE, age=20, name=Eason]
* Person [gender=MALE, age=20, name=Jack]
* Person [gender=FEMALE, age=10, name=Lucy]
* Person [gender=FEMALE, age=20, name=Lily]
*
*/
// List可直接排序，传入compareTo方法引用
List personsNew = new ArrayList<>(persons);
personsNew.sort(Person::compareTo);
// 2. 使用比较器链，排序方式更灵活
persons.sort(Comparator.comparing(Person::getAge).thenComparing(Person::getGender).thenComparing(Person::getName));
/*
* Person [gender=MALE, age=10, name=John]
* Person [gender=FEMALE, age=10, name=Lucy]
* Person [gender=MALE, age=20, name=Eason]
* Person [gender=MALE, age=20, name=Jack]
* Person [gender=FEMALE, age=20, name=Lily]
*
*/
}
static void method5() {
// 分组与分区
// 分组
Map> grouped1 = persons.stream().collect(Collectors.groupingBy(Person::getGender));
// 子分组，多个分组
Map>> grouped2 = persons.stream()
.collect(Collectors.groupingBy(Person::getGender, LinkedHashMap::new,
Collectors.groupingBy(Person::getAge, LinkedHashMap::new, Collectors.toList())));
// --------------------------------------------------------------------------------
// 分区
Map> partitioned1 = persons.stream().collect(Collectors.partitioningBy(person -> person.getAge() <= 6));
// 分区并计数
Map partitioned2 = persons.stream().collect(Collectors.partitioningBy(person -> person.getAge() <= 6, Collectors.counting()));
}
static void method6() {
// 归约 reduce:"减少，缩小(尺寸、数量、价格等);(使)蒸发;减轻体重;节食"
// 数字
Integer reduced1 = numbers.stream().reduce((x, y) -> x + y).get();
System.out.println(reduced1);// 15
// 数字，指定初始值
Integer reduced2 = numbers.stream().reduce(0, (x, y) -> x + y);
System.out.println(reduced1);// 15
// 字符串拼接
String reduced3 = strs.stream().reduce((s1, s2) -> s1 + s2).get();
System.out.println(reduced3);// b2b1a2cba
// 字符串拼接，指定前缀
String reduced4 = strs.stream().reduce("prefix", (s1, s2) -> s1 + s2);
System.out.println(reduced4);// prefixb2b1a2cba
// --------------------------------------------------------------------------------
// 数字，求最小值
Integer min = numbers.stream().reduce(Math::min).get();
System.out.println(min);
// 数字，求最大值
Integer max = numbers.stream().reduce(Math::max).get();
System.out.println(max);
// 数字，求和
Integer sum = numbers.stream().reduce(Integer::sum).get();
System.out.println(sum);
// --------------------------------------------------------------------------------
// 实现流的拼接 list集合里面是list集合
Stream reduced5 = strsList.stream().map(list -> list.stream()).reduce(Stream::concat).get();
List reducedCollect5 = reduced5.collect(Collectors.toList());
System.out.println(reducedCollect5);
}
static void method7() {
// findFirst 返回第一个符合条件
strs.stream().filter(str -> str.length() > 10).findFirst().get();
// findAny 返回任意一个符合条件，串行流和findFirst相同，并行流返回最先有值的线程
strs.stream().filter(str -> str.length() > 10).findAny().get();
// anyMatch 任意符合
boolean flag1 = strs.stream().anyMatch(str -> str.length() > 10);
// allMatch 全部符合
boolean flag2 = strs.stream().allMatch(str -> str.length() > 10);
// noneMatch 全不符合
boolean flag3 = strs.stream().noneMatch(str -> str.length() > 10);
// --------------------------------------------------------------------------------
// distinct 去重
strs.stream().distinct();
// count 计数
strs.stream().filter(str -> str.length() > 10).count();
// skip 跳过
strs.stream().filter(str -> str.length() > 10).skip(3);
// limit 限定数量
strs.stream().filter(str -> str.length() > 10).limit(3);
// --------------------------------------------------------------------------------
// 遍历
strs.stream().forEach(System.out::println);
}
static void method8() {
// IntStream
// 使用IntStream生成50个连续字符
IntStream.range(0, 50).mapToObj(s -> "*").collect(Collectors.joining());
IntStream.range(0, 50).mapToObj(s -> "*").collect(Collectors.joining(""));
IntStream.rangeClosed(1, 50).mapToObj(s -> "*").reduce((s1, s2) -> s1 + s2).get();
IntStream.rangeClosed(1, 50).mapToObj(s -> "*").reduce(new StringJoiner("", "[", "]"), StringJoiner::add, StringJoiner::merge);
// 生成随机数
Random random = new Random();
IntStream.generate(random::nextInt);
// 生成特定元素
IntStream.iterate(1, i -> i * 2);
}
static class Person implements Comparable {
private GenderEnum gender;
private int age;
private String name;
public Person(GenderEnum gender, int age, String name) {
this.gender = gender;
this.age = age;
this.name = name;
}
public GenderEnum getGender() {
return gender;
}
public void setGender(GenderEnum gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int compareTo(Person o) {
if (this.gender != o.gender) {
return this.gender.compareTo(o.gender);
}
if (this.age != o.age) {
return this.age - o.age;
}
return this.name.compareTo(o.name);
}
@Override
public String toString() {
return "Person [gender=" + gender + ", age=" + age + ", name=" + name + "]";
}
}
enum GenderEnum {
MALE, FEMALE
}
static class Item {
private String itemId;
private String name;
private String value;
private List subItems;
public Item(String itemId, String name) {
this.itemId = itemId;
this.name = name;
}
public String getItemId() {
return itemId;
}
public void setItemId(String itemId) {
this.itemId = itemId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
public List getSubItems() {
return subItems;
}
public void setSubItems(List subItems) {
this.subItems = subItems;
}
@Override
public String toString() {
return "Item [itemId=" + itemId + ", name=" + name + ", value=" + value + ", subItems=" + subItems + "]";
}
}
public static void main(String[] args) {
// method5();
method6();
}
}
