package com.carl;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import static java.util.stream.Collectors.joining;
public class CollectionsTest {
public static Predicate<String> checkSize(final int size) {
return s -> s.length() > size;
}
public static void main(String[] args) {
List<String> list = Arrays.asList("a", "ac");
List<String> personList = Arrays.asList("p01", "p02", "p03");
list.forEach(new Consumer<Object>() {
@Override
public void accept(Object t) {
System.out.println(t);
}
});
System.out.println("----");
list.forEach(System.out::println);
System.out.println("----");
list.stream().map(s -> s.toUpperCase()).forEach(System.out::println);
list.stream().map(String::toUpperCase).forEach(System.out::println);
System.out.println("----");
list.stream().map(s -> s.length()).forEach(System.out::println);
System.out.println("----");
list.stream().filter(s -> s.length()>1).forEach(System.out::println);
System.out.println("----");
final Predicate<String> filterPolicy = s -> s.length() > 1;
list.stream().filter(filterPolicy).forEach(System.out :: println);
personList.stream().filter(filterPolicy).forEach(System.out :: println);
System.out.println("----");
System.out.println(list.stream().filter(filterPolicy).count());
System.out.println("----");
personList.stream().filter(checkSize(2)).forEach(System.out :: println);
System.out.println("----");
// final Function<Integer, Predicate<String>> checkSizeFun = (Integer size) -> {
// Predicate<String> checkSize = (String s) -> s.length() > size;
// return checkSize;
// };
final Function<Integer, Predicate<String>> checkSizeFun = size -> s -> s.length() > size;
personList.stream().filter(checkSizeFun.apply(2)).forEach(System.out :: println);
System.out.println("----");
Optional<String> firstResult = personList.stream().filter(checkSizeFun.apply(3)).findFirst();
System.out.println(firstResult.orElse("No found"));
firstResult = personList.stream().filter(checkSizeFun.apply(2)).findFirst();
firstResult.ifPresent(s -> System.out.println(s + " is found"));
System.out.println("----");
System.out.println("Total size:" + personList.stream().mapToInt(s -> s.length()).sum());
System.out.println("----");
//final Optional<String> findOneByReduce = personList.stream().reduce((s1, s2) -> s1.length() >= s2.length() ? s1 : s2);
final Optional<String> findOneByReduce = personList.stream().reduce((s1, s2) -> {
System.out.print("s1:" + s1);
System.out.println(", s2:" + s2);
return s1.length() >= s2.length() ? s1 : s2;
});
findOneByReduce.ifPresent(s -> System.out.println(s));
System.out.println("----");
//final String optionalReduce = personList.stream().reduce("p0", (s1, s2) -> s1.length() >= s2.length() ? s1 : s2);
final String optionalReduce = personList.stream().reduce("p0", (s1, s2) -> {
System.out.print("s1:" + s1);
System.out.println(", s2:" + s2);
return s1.length() >= s2.length() ? s1 : s2;
});
System.out.println(optionalReduce);
// String reduceResult = "p0";
// for (String s : personList) {
// System.out.println(reduceResult.length() >= s.length());
// }
System.out.println("----");
System.out.println(String.join(",", list));
System.out.println("----");
System.out.println(list.stream().map(String::toUpperCase).collect(joining(",")));
}
}
package com.carl;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.stream.Collectors;
import static java.util.stream.Collectors.reducing;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.toList;
import static java.util.Comparator.comparing;
import com.carl.beans.Person;
public class StringsComparatorsFilters {
private static void printC(int c) {
System.out.println((char)c);
}
public static void main(String[] args) {
final String str = "wa68";
str.chars().forEach(c -> System.out.println(c));
System.out.println("---------------");
str.chars().forEach(System.out::println);
System.out.println("---------------");
str.chars().forEach(StringsComparatorsFilters::printC);
System.out.println("---------------");
str.chars().mapToObj(c -> Character.valueOf((char)c)).forEach(System.out::println);
System.out.println("---------------");
str.chars().filter(c -> Character.isDigit(c)).forEach(c -> printC(c));
str.chars().filter(Character::isDigit).forEach(StringsComparatorsFilters::printC);
System.out.println("---------------");
final List<Person> people = Arrays.asList(
new Person("jx", 24),
new Person("hh", 21),
new Person("jj", 24),
new Person("ss", 28));
// people.add(new Person("wu", 27)); //java.lang.UnsupportedOperationException
// asList 的返回对象是一个 Arrays 内部类，并没有实现集合的修改方法。 Arrays . asList体现的是适配器模式，只是转换接口，后台的数据仍是数组
people.stream().sorted((p1, p2) -> p1.ageDiff(p2)).forEach(System.out::println);
System.out.println("---------------");
people.stream().sorted(Person::ageDiff).forEach(System.out::println);
System.out.println("---------------");
Comparator<Person> compareAscending = (p1, p2) -> p1.ageDiff(p2);
Comparator<Person> compareDscending = compareAscending.reversed();
people.stream().sorted(compareDscending).forEach(System.out::println);
System.out.println("---------------");
people.stream().sorted((p1, p2) -> p1.getName().compareToIgnoreCase(p2.getName())).forEach(System.out::println);
System.out.println("---------------");
people.stream().min(Person::ageDiff).ifPresent(youngest -> System.out.println("Youngest:" + youngest));
people.stream().max(Person::ageDiff).ifPresent(eldest -> System.out.println("Eldest:" + eldest));
System.out.println("---------------");
final Function<Person, String> byName = p -> p.getName();
people.stream().sorted(comparing(byName)).forEach(System.out::println);
System.out.println("---------------");
final Function<Person, Integer> byAge = p -> p.getAge();
people.stream().sorted(comparing(byAge)).forEach(System.out::println);
System.out.println("---------------");
people.stream().sorted(comparing(byAge).thenComparing(byName)).forEach(System.out::println);
System.out.println("---------------");
List<Person> oldThan25 = people.stream().filter(p -> p.getAge() > 25).collect(Collectors.toList());
oldThan25.forEach(System.out::println);
System.out.println("---------------");
Map<Integer, List<Person>> peopleByAge = people.stream().collect(Collectors.groupingBy(Person::getAge));
System.out.println(peopleByAge);
System.out.println("---------------");
Map<Integer, List<String>> nameOfPeopleByAge = people.stream().collect(groupingBy(Person::getAge, mapping(Person::getName, toList())));
System.out.println(nameOfPeopleByAge);
System.out.println("---------------");
Map<Integer, Long> coutPeopleByAge = people.stream().collect(groupingBy(Person::getAge, counting()));
System.out.println(coutPeopleByAge);
System.out.println("---------------");
Comparator<Person> compareByAge = Comparator.comparing(Person::getAge);
Map<Character, Optional<Person>> oldestPersonOfEachLetter = people.stream().collect(groupingBy(p -> p.getName().charAt(0),
reducing(BinaryOperator.maxBy(compareByAge))));
System.out.println(oldestPersonOfEachLetter);
}
}
就是新的 API 学习了，然后好多对集合的操作
《Functional.Programming.in.Java》