stream2

import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

public class MyListCollector<T> implements Collector<T, List<T>, List<T>>{

    @Override
    public Supplier<List<T>> supplier() {
        return ArrayList<T>::new;
    }

    @Override
    public BiConsumer<List<T>, T> accumulator() {
//        return ArrayList<T>::add;
        return List::add;
    }

    @Override
    public BinaryOperator<List<T>> combiner() {
        return null;
    }

    @Override
    public Function<List<T>, List<T>> finisher() {
        return null;
    }

    @Override
    public Set<Characteristics> characteristics() {
        return null;
    }
}

import java.util.Arrays;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

import static java.util.stream.Collector.Characteristics.CONCURRENT;
import static java.util.stream.Collector.Characteristics.IDENTITY_FINISH;
import static java.util.stream.Collector.Characteristics.UNORDERED;

public class MySetCollector<T> implements Collector<T, Set<T>, Set<T>> {

    @Override
    public Supplier<Set<T>> supplier() {
        System.out.println("supplier");
        return HashSet<T>::new;
    }

    // 如果return HashSet<T>::add，那么會編譯報錯，原因在於
    // 如果這里return的是HashSet，而supplier方法返回的是TreeSet
    // 那么顯然，中間用於累積的容器的類型二者是不一致的；就會出現問題
    // 如果這里使用了Set::add，即接口類型，那么它就會兼容於supplier
    // 所返回的容器類型
    // 總之：這里return的類型必須要與泛型的類型保持完全一致
    @Override
    public BiConsumer<Set<T>, T> accumulator() {
        System.out.println("accumulator");
//        return Set<T>::add;

        return (set, item) -> {
            System.out.println(item + ", " + set + ", " + Thread.currentThread().getName() );
            set.add(item);
        };
    }

    @Override
    public BinaryOperator<Set<T>> combiner() {
        System.out.println("combiner");

        return (set1, set2) -> {
            set1.addAll(set2);
            return set1;
        };
    }

    @Override
    public Function<Set<T>, Set<T>> finisher() {
        System.out.println("finisher");

        return Function.identity();

//        對於IDENTITY_FINISH來說，該方法可以直接拋出異常，該方法實際上並不會被調用
//        throw new UnsupportedOperationException();
    }

    // 該方法會被調用2次，分別用於確定UNORDERED與IDENTITY_FINISH
    @Override
    public Set<Characteristics> characteristics() {
        System.out.println("characteristics");

        return Collections.unmodifiableSet(EnumSet.of(IDENTITY_FINISH, CONCURRENT, UNORDERED));
    }

    public static void main(String[] args) {
        List<String> list = Arrays.asList("hello", "world", "welcome", "hello", "a", "b", "c", "d", "e", "f", "g", "aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh", "ii");
        Set<String> preSet = new HashSet<>();
        preSet.addAll(list);

        System.out.println(preSet);



        Set<String> set = preSet.stream().parallel().collect(new MySetCollector<>());

        System.out.println("---------------");

        System.out.println(set);




//        System.out.println(Runtime.getRuntime().availableProcessors());
    }
}

import java.util.Arrays;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

public class MySetCollector2<T> implements Collector<T, Set<T>, Map<T, T>> {

    @Override
    public Supplier<Set<T>> supplier() {
        System.out.println("supplier invoked!");

        // 串行流調用時，只會生成一個HashSet
        // 並行流調用時，每個線程都會生成一個HashSet
        /**
         * *   A a1 = supplier.get();
         *     accumulator.accept(a1, t1);
         *     accumulator.accept(a1, t2);
         *     R r1 = finisher.apply(a1);  // result without splitting
         *
         *     A a2 = supplier.get();
         *     accumulator.accept(a2, t1);
         *     A a3 = supplier.get();
         *     accumulator.accept(a3, t2);
         *     R r2 = finisher.apply(combiner.apply(a2, a3));  // result with splitting
         */

        return () -> {
            System.out.println("~~~~~~~~~~~~~~~~~");
            return new HashSet<T>();
        };

//        return HashSet<T>::new;
    }

    @Override
    public BiConsumer<Set<T>, T> accumulator() {
        System.out.println("accumulator invoked!");

        return (set, item) -> {
            System.out.println("accumulator, " + set + ", " + Thread.currentThread().getName());
            set.add(item);
        };
    }

    @Override
    public BinaryOperator<Set<T>> combiner() {
        System.out.println("combiner invoked!");

        return (set1, set2) -> {
            System.out.println("combiner, " + set1 + ", " + set2);
            set1.addAll(set2);
            return set1;
        };
    }

    @Override
    public Function<Set<T>, Map<T, T>> finisher() {
        System.out.println("finisher invoked!");

        return set -> {
            System.out.println("finisher, " + set);
            Map<T, T> map = new TreeMap<>();
            set.stream().forEach(item -> map.put(item, item));
            return map;
        };
    }

    @Override
    public Set<Characteristics> characteristics() {
        System.out.println("characteristics invoked!");
//        return Collections.unmodifiableSet(EnumSet.of(Characteristics.UNORDERED, Characteristics.IDENTITY_FINISH));
        return Collections.unmodifiableSet(EnumSet.of(Characteristics.UNORDERED, Characteristics.CONCURRENT));
    }

    public static void main(String[] args) {
        System.out.println(Runtime.getRuntime().availableProcessors());

        List<String> list = Arrays.asList("hello", "world", "welcome", "hello", "a", "b", "c", "d", "e", "f", "g");
        Set<String> set = new HashSet<>();
        set.addAll(list);

        System.out.println("set: " + set);

        System.out.println("----------");

        //串行執行時combiner並不會得到調用，combiner只在並行流時會得到調用
//        Map<String, String> map = set.stream().parallel().sequential().parallel().collect(new MySetCollector2<>());
        Map<String, String> map = set.parallelStream().collect(new MySetCollector2<>());
        System.out.println(map);
    }
}

import java.util.Arrays;
import java.util.Comparator;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import static java.util.stream.Collectors.averagingInt;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.maxBy;
import static java.util.stream.Collectors.minBy;
import static java.util.stream.Collectors.partitioningBy;
import static java.util.stream.Collectors.summarizingInt;
import static java.util.stream.Collectors.summingInt;
import static java.util.stream.Collectors.toList;

public class StreamTest1 {

    public static void main(String[] args) {
        Student student1 = new Student("zhangsan", 80);
        Student student2 = new Student("lisi", 90);
        Student student3 = new Student("wangwu", 100);
        Student student4 = new Student("zhaoliu", 90);
        Student student5 = new Student("zhaoliu", 90);

        List<Student> students = Arrays.asList(student1, student2, student3, student4, student5);

//        List<Student> students1 = students.stream().collect(toList());
//        students1.forEach(System.out::println);
//        System.out.println("------------");
//
//
//        System.out.println("count: " + students.stream().collect(counting()));
//        System.out.println("count: " + students.stream().count());
//        System.out.println("------------");
//
//
//        students.stream().collect(minBy(Comparator.comparingInt(Student::getScore))).ifPresent(System.out::println);
//
//        students.stream().collect(maxBy(Comparator.comparingInt(Student::getScore))).ifPresent(System.out::println);
//
//        System.out.println(students.stream().collect(averagingInt(Student::getScore)));
//
//        System.out.println(students.stream().collect(summingInt(Student::getScore)));
//
//        IntSummaryStatistics intSummaryStatistics = students.stream().collect(summarizingInt(Student::getScore));
//        System.out.println(intSummaryStatistics);
//        System.out.println("------------");
//
//        System.out.println(students.stream().map(Student::getName).collect(joining()));
//        System.out.println(students.stream().map(Student::getName).collect(joining(", ")));
//        System.out.println(students.stream().map(Student::getName).collect(joining(", ", "<begin> ", " <end>")));
//        System.out.println("------------");
//


//        Map<Integer, Map<String, List<Student>>> map = students.stream().
//                collect(groupingBy(Student::getScore, groupingBy(Student::getName)));
//        System.out.println(map);
//        System.out.println("------------");


//
//        Map<Boolean, List<Student>> map2 = students.stream().
//                collect(partitioningBy(student -> student.getScore() > 80));
//        System.out.println(map2);
//        System.out.println("------------");
//


//        Map<Boolean, Map<Boolean, List<Student>>> map3 = students.stream().
//                collect(partitioningBy(student -> student.getScore() > 80,
//                        partitioningBy(student -> student.getScore() > 90)));
//        System.out.println(map3);
//        System.out.println("------------");


//
//        Map<Boolean, Long> map4 = students.stream().
//                collect(partitioningBy(student -> student.getScore() > 80, counting()));
//        System.out.println(map4);
//        System.out.println("------------");
////
//        Map<String, Student> map5 = students.stream().
//                collect(groupingBy(Student::getName,
//                        collectingAndThen(minBy(Comparator.comparingInt(Student::getScore)),
//                        Optional::get)));
//        System.out.println(map5);
    }
}

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class StreamTest2 {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("nihao", "hello", "world", "welcome");

//        Collections.sort(list, (item1, item2) -> item1.length() - item2.length());
//        Collections.sort(list, (item1, item2) -> item2.length() - item1.length());

//        Collections.sort(list, Comparator.comparingInt(String::length).reversed());
////         此處lambda參數的類型推斷無法推斷出item為String類型，需要顯式指定；原因在於這是一個獨立的參數，並不是通過list調用方法來得出的
//        Collections.sort(list, Comparator.comparingInt((String item) -> item.length()).reversed());
////         如下代碼無法編譯通過，因為lambda參數要求參數類型應該是String或是String的父類，而Boolean則不是
//        Collections.sort(list, Comparator.comparingInt((Boolean item) -> 1).reversed());

////         Collections的sort就是調用List的sort實現的
//        list.sort(Comparator.comparingInt(String::length).reversed());
////         如下代碼必須要顯式聲明item的類型為String
//        list.sort(Comparator.comparingInt((String item) -> item.length()).reversed());
//
//
//        Collections.sort(list, Comparator.comparingInt(String::length).thenComparing(String.CASE_INSENSITIVE_ORDER));
//
//        // 為何下面這個thenComparing中的參數類型可以推斷出來？
//        Collections.sort(list, Comparator.comparingInt(String::length).
//                thenComparing((item1, item2) -> item1.toLowerCase().compareTo(item2.toLowerCase())));
//        Collections.sort(list, Comparator.comparingInt(String::length).
//                thenComparing(Comparator.comparing(String::toLowerCase)));
//        Collections.sort(list, Comparator.comparingInt(String::length).
//                thenComparing(Comparator.comparing(String::toLowerCase, Comparator.reverseOrder())));
////
//        // welcome, world, nihao, hello
//        Collections.sort(list, Comparator.comparingInt(String::length).reversed().
//                thenComparing(Comparator.comparing(String::toLowerCase, Comparator.reverseOrder())));
//
//        // welcome, world, nihao, hello, 注意：thenComparing都是根據前一個compare的結果來決定此次是否進行再次排序，
//        // 如果前一次排序不返回0，那么此次排序結果就直接返回之前的排序結果

        Collections.sort(list, Comparator.comparingInt(String::length).reversed().
                thenComparing(Comparator.comparing(String::toLowerCase, Comparator.reverseOrder())).
                thenComparing(Comparator.reverseOrder()));

        System.out.println(list);
    }
}

public class Student {

    private String name;

    private int score;

    public Student(String name, int score) {
        this.name = name;
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", score=" + score +
                '}';
    }
}