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March 9, 2018 09:41
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java8-stream
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import com.google.gson.Gson; | |
import com.zeusro.Person; | |
import com.zeusro.Sex; | |
import java.time.LocalDate; | |
import java.time.ZoneId; | |
import java.util.*; | |
import java.util.stream.Collectors; | |
import java.util.stream.Stream; | |
import static java.lang.System.out; | |
/** | |
* The type Main <p/> | |
* author: <a href="http://zeusro.github.io/">Zeusro</a> <p/> | |
* | |
* @date Created in 2018.03.09 <p/> | |
*/ | |
public class Main { | |
private static Date convertLocalDateToTimeZone(LocalDate localDate) { | |
ZoneId zoneID = ZoneId.systemDefault(); | |
return Date.from(localDate.atStartOfDay(zoneID).toInstant()); | |
} | |
public static void main(String[] args) { | |
try { | |
// LocalDate.of(2018, 02, 29); | |
//java.time.DateTimeException: Invalid date 'February 29' as '2018' is not a leap year | |
final Person female = new Person(); | |
female.setBirthday(convertLocalDateToTimeZone(LocalDate.of(1981, 1, 1))); | |
female.setHeight(165); | |
female.setWeight(50); | |
female.setSex(Sex.Female); | |
female.setAddress("北京"); | |
female.setIdentifier("1"); | |
female.setHobbies(new ArrayList<String>() {{ | |
add("吃飯"); | |
add("逛街"); | |
}}); | |
final Person male = new Person(); | |
male.setBirthday(convertLocalDateToTimeZone(LocalDate.of(1982, 2, 1))); | |
male.setHeight(170); | |
male.setWeight(50); | |
male.setSex(Sex.Male); | |
male.setAddress("北京"); | |
male.setIdentifier("2"); | |
male.setHobbies(new ArrayList<String>() {{ | |
add("吃飯"); | |
add("看電影"); | |
}}); | |
final Person x = new Person(); | |
x.setBirthday(convertLocalDateToTimeZone(LocalDate.of(1983, 3, 1))); | |
x.setHeight(170); | |
x.setWeight(50); | |
x.setSex(Sex.X); | |
x.setAddress("北京"); | |
x.setIdentifier("3"); | |
x.setHobbies(new ArrayList<String>() {{ | |
add("吃飯"); | |
add("上網"); | |
}}); | |
final Person male2 = new Person(); | |
male2.setBirthday(convertLocalDateToTimeZone(LocalDate.of(1984, 1, 1))); | |
male2.setHeight(150); | |
male2.setWeight(35); | |
male2.setSex(Sex.Male); | |
male2.setAddress("北京"); | |
male2.setIdentifier("4"); | |
male2.setHobbies(new ArrayList<String>() {{ | |
add("吃飯"); | |
add("看電影"); | |
}}); | |
List<Person> list1 = new ArrayList<Person>() { | |
{ | |
add(female); | |
add(male); | |
add(x); | |
} | |
}; | |
List<Person> list2 = new ArrayList<Person>() { | |
{ | |
add(female); | |
add(male2); | |
} | |
}; | |
//流只能用一次,重复使用会导致以下异常 | |
//java.lang.IllegalStateException: stream has already been operated upon or closed | |
Stream<Person> list1Stream = list1.stream(); | |
Date time1 = convertLocalDateToTimeZone(LocalDate.of(1990, 1, 1)); | |
//0 | |
Long count1 = list1.stream().filter(o -> o.getBirthday().equals(time1)).count(); | |
Map<Sex, List<Person>> group1 = list1.stream().collect(Collectors.groupingBy(Person::getSex)); | |
Iterator it = group1.entrySet().iterator(); | |
while (it.hasNext()) { | |
Map.Entry<Sex, List<Person>> groupByItem = (Map.Entry) it.next(); | |
Sex sex = groupByItem.getKey(); | |
out.println(sex); | |
groupByItem.getValue().forEach(person -> { | |
out.println(new Gson().toJson(person)); | |
}); | |
} | |
/* | |
输出结果: | |
Male | |
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"Male"} | |
Female | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"Female"} | |
X | |
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"} | |
*/ | |
//stream没有RemoveAll的操作 | |
Person after90 = list1.stream() | |
.filter(o -> o.getBirthday().after(convertLocalDateToTimeZone(LocalDate.of(1990, 1, 1)))) | |
.findFirst() | |
.orElse(null); | |
// null | |
list1.stream().forEach(o -> { | |
//在ForEach當中可對集合進行操作 | |
o.setSex(Sex.X); | |
}); | |
list1.forEach(o -> { | |
out.println(new Gson().toJson(o)); | |
}); | |
/* | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"} | |
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"} | |
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"} | |
*/ | |
//IntStream的max方法返回的是OptionalInt,要先判断有没有值再读取值.isPresent=false 时直接getAsInt会报错.mapToLong,mapToDouble同理 | |
OptionalInt maxHeightOption = list1.stream().mapToInt(Person::getHeight).max(); | |
//字符串拼接、数值的 sum、min、max、average 都是特殊的 reduce。 | |
//当集合为长度0的集合时会返回起始值Integer.MIN_VALUE,起始值也不能乱传,个中缘由我暂不清楚 | |
int maxHeight = list1.stream().mapToInt(Person::getHeight).reduce(Integer.MIN_VALUE, Integer::max); | |
out.println(maxHeight); | |
//170 | |
if (maxHeightOption.isPresent()) { | |
maxHeight = maxHeightOption.getAsInt(); | |
out.println(maxHeight); | |
//170 | |
} | |
//mapToInt参数的2种写法都一样,我比较喜欢以下写法,但是 idea 会报 warning | |
OptionalInt minWeightOption = list1.stream().mapToInt(o -> o.getHeight()).min(); | |
int minWeight = list1.stream().mapToInt(o -> o.getHeight()).reduce(Integer.MAX_VALUE, Integer::min); | |
list1.stream().map(Person::getIdentifier).distinct(); | |
//skip和 limit参数都是long, 这个要注意 | |
list1.stream().skip(1L).limit(2L); | |
out.println("------------------------------------|升序|------------------------------------"); | |
list1 = list1.stream().sorted(Comparator.comparing(Person::getBirthday)).collect(Collectors.toList()); | |
out.println(new Gson().toJson(list1)); | |
list1 = list1.stream().sorted((left, right) -> left.getBirthday().compareTo(right.getBirthday())).collect(Collectors.toList()); | |
out.println(new Gson().toJson(list1)); | |
/* | |
[{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"},{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"},{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"}] | |
[{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"},{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"},{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"}] | |
*/ | |
out.println("------------------------------------|降序|------------------------------------"); | |
list1 = list1.stream().sorted(Comparator.comparing(Person::getBirthday).reversed()).collect(Collectors.toList()); | |
out.println(new Gson().toJson(list1)); | |
list1 = list1.stream().sorted((left, right) -> right.getBirthday().compareTo(left.getBirthday())).collect(Collectors.toList()); | |
out.println(new Gson().toJson(list1)); | |
/* | |
[{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"},{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"},{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"}] | |
[{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"},{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"},{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"}] | |
*/ | |
out.println("------------------------------------|交集 list1 ∩ list2|------------------------------------"); | |
list1.stream().filter(o -> list2.contains(o)).collect(Collectors.toList()); | |
out.println("------------------------------------|并集list1 ∪ list2 |------------------------------------"); | |
list1.addAll(list2); | |
list1.stream().distinct().collect(Collectors.toList()); | |
out.println("------------------------------------|差集list1 - list2|------------------------------------"); | |
list1.stream().filter(item1 -> !list2.contains(item1)).collect(Collectors.toList()); | |
out.println("------------------------------------|数据结构转换|------------------------------------"); | |
List<Person> list3 = list1.stream().filter(o -> true).collect(Collectors.toList()); | |
ArrayList<Person> list4 = list1.stream().filter(o -> true).collect(Collectors.toCollection(ArrayList::new)); | |
Set<Person> list5 = list1.stream().filter(o -> true).collect(Collectors.toSet()); | |
Object[] list6 = list1.stream().toArray(); | |
Person[] list7 = list1.stream().toArray(Person[]::new); | |
out.println("------------------------------------|其他需要注意的地方|------------------------------------"); | |
//2个数组合并用这种方法的话, list2会为空 | |
Stream.of(list1, list2).collect(Collectors.toList()); | |
//以下才是正确用法 | |
Stream.of(list1, list2).flatMap(List::stream).collect(Collectors.toList()); | |
out.println("------------------------------------|reduce|------------------------------------"); | |
//字符串拼接、数值的 sum、min、max、average 都是特殊的 reduce。 | |
maxHeight = list1.stream().mapToInt(Person::getHeight).reduce(Integer.MIN_VALUE, Integer::max); | |
minWeight = list1.stream().mapToInt(o -> o.getHeight()).reduce(Integer.MAX_VALUE, Integer::min); | |
int sumWeight = -1; | |
OptionalInt sumWeightOption = list1.stream().mapToInt(Person::getHeight).reduce(Integer::sum); | |
if (sumWeightOption.isPresent()) { | |
sumWeight = sumWeightOption.getAsInt(); | |
} | |
sumWeight = list1.stream().mapToInt(Person::getHeight).reduce(0, (a, b) -> a + b); | |
sumWeight = list1.stream().mapToInt(Person::getHeight).reduce(0, Integer::sum); | |
out.println("------------------------------------|peek ,forEach ,forEachOrdered |------------------------------------"); | |
out.println("forEach后面无法继续执行方法"); | |
list1.stream().forEach(o -> { | |
out.println(new Gson().toJson(o)); | |
}); | |
/* | |
forEach后面无法继续执行方法 | |
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"} | |
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"} | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"} | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"} | |
{"height":150,"weight":35,"identifier":"4","address":"北京","birthday":"Jan 1, 1984 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"Male"} | |
*/ | |
out.println("先排序,然后遍历"); | |
list1.stream().forEachOrdered(o -> { | |
out.println(new Gson().toJson(o)); | |
}); | |
/* | |
先排序,然后遍历 | |
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"} | |
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"} | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"} | |
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"} | |
{"height":150,"weight":35,"identifier":"4","address":"北京","birthday":"Jan 1, 1984 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"Male"} | |
*/ | |
out.println("peek*2"); | |
List<Integer> l = Stream.iterate(0, (Integer n) -> n + 1) //生成一个每次递增1的等差数列 | |
.peek(n -> out.println("number generated:" + n)) | |
.filter(n -> (n % 2 == 0)) | |
.peek(n -> out.println("Even number filter passed for" + n)) //遇到偶数时继续输出 | |
.limit(5).collect(Collectors.toList()); | |
out.println(new Gson().toJson(l)); | |
//可以看到在生成到9时,这个操作结束了,是因为设置了limit | |
/* | |
peek*2 | |
number generated:0 | |
Even number filter passed for0 | |
number generated:1 | |
number generated:2 | |
Even number filter passed for2 | |
number generated:3 | |
number generated:4 | |
Even number filter passed for4 | |
number generated:5 | |
number generated:6 | |
Even number filter passed for6 | |
number generated:7 | |
number generated:8 | |
Even number filter passed for8 | |
[0,2,4,6,8] | |
*/ | |
} catch (Exception e) { | |
out.println(e); | |
} finally { | |
out.println("done"); | |
} | |
} | |
} |
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package com.zeusro; | |
import java.util.Date; | |
import java.util.List; | |
/** | |
* The type Person <p/> | |
* author: <a href="http://zeusro.github.io/">Zeusro</a> <p/> | |
* | |
* @date Created in 2018.03.08 <p/> | |
*/ | |
public class Person implements Cloneable { | |
// 身高 | |
private int height; | |
//体重- | |
private int weight; | |
//身份证号 | |
private String identifier; | |
//地址 | |
private String address; | |
//生日 | |
private Date birthday; | |
//爱好 | |
private List<String> hobbies; | |
//性别 | |
private Sex sex; | |
@Override | |
protected Object clone() throws CloneNotSupportedException { | |
return (Person) super.clone(); | |
} | |
public Sex getSex() { | |
return sex; | |
} | |
public void setSex(Sex sex) { | |
this.sex = sex; | |
} | |
public String getAddress() { | |
return address; | |
} | |
public void setAddress(String address) { | |
this.address = address; | |
} | |
public Date getBirthday() { | |
return birthday; | |
} | |
public void setBirthday(Date birthday) { | |
this.birthday = birthday; | |
} | |
public int getHeight() { | |
return height; | |
} | |
public void setHeight(int height) { | |
this.height = height; | |
} | |
public List<String> getHobbies() { | |
return hobbies; | |
} | |
public void setHobbies(List<String> hobbies) { | |
this.hobbies = hobbies; | |
} | |
public String getIdentifier() { | |
return identifier; | |
} | |
public void setIdentifier(String identifier) { | |
this.identifier = identifier; | |
} | |
public int getWeight() { | |
return weight; | |
} | |
public void setWeight(int weight) { | |
this.weight = weight; | |
} | |
} |
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package com.zeusro; | |
public enum Sex { | |
//男 | |
Male, | |
//女 | |
Female, | |
//第三性 https://zh.wikipedia.org/wiki/%E7%AC%AC%E4%B8%89%E6%80%A7 | |
X, | |
} |
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