java8(3) sorted的使用

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package java.util;

import java.io.Serializable;
import java.util.function.Function;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;
import java.util.function.ToDoubleFunction;
import java.util.Comparators;


@FunctionalInterface
public interface Comparator<T> {
    int compare(T o1, T o2);
    boolean equals(Object obj);
    default Comparator<T> reversed() {
        return Collections.reverseOrder(this);
    }
    default Comparator<T> thenComparing(Comparator<? super T> other) {
        Objects.requireNonNull(other);
        return (Comparator<T> & Serializable) (c1, c2) -> {int res = compare(c1, c2);
        return (res != 0) ? res : other.compare(c1, c2);
        };
    }
    
    default <U> Comparator<T> thenComparing(
            Function<? super T, ? extends U> keyExtractor,
            Comparator<? super U> keyComparator){
        return thenComparing(comparing(keyExtractor, keyComparator));
    }

    
    default <U extends Comparable<? super U>> Comparator<T> thenComparing(
            Function<? super T, ? extends U> keyExtractor) {
        return thenComparing(comparing(keyExtractor));
    }

 
    default Comparator<T> thenComparingInt(ToIntFunction<? super T> keyExtractor) {
        return thenComparing(comparingInt(keyExtractor));
    }

    default Comparator<T> thenComparingLong(ToLongFunction<? super T> keyExtractor) {
        return thenComparing(comparingLong(keyExtractor));
    }

    default Comparator<T> thenComparingDouble(ToDoubleFunction<? super T> keyExtractor) {
        return thenComparing(comparingDouble(keyExtractor));
    }

 
    public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() {
        return Collections.reverseOrder();
    }


    @SuppressWarnings("unchecked")
    public static <T extends Comparable<? super T>> Comparator<T> naturalOrder() {
        return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE;
    }


    public static <T> Comparator<T> nullsFirst(Comparator<? super T> comparator) {
        return new Comparators.NullComparator<>(true, comparator);
    }


    public static <T> Comparator<T> nullsLast(Comparator<? super T> comparator) {
        return new Comparators.NullComparator<>(false, comparator);
    }

    public static <T, U> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor,Comparator<? super U> keyComparator){
        Objects.requireNonNull(keyExtractor);
        Objects.requireNonNull(keyComparator);
        return (Comparator<T> & Serializable)(c1, c2) -> keyComparator.compare(keyExtractor.apply(c1), keyExtractor.apply(c2));
    }

    public static <T, U extends Comparable<? super U>> Comparator<T> comparing(
            Function<? super T, ? extends U> keyExtractor){
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)(c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
    }

    public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor) {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)(c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1)keyExtractor.applyAsInt(c2));
    }
    public static <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor) {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)(c1, c2) -> Long.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2));
    }
    public static<T> Comparator<T> comparingDouble(ToDoubleFunction<? super T> keyExtractor) {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)(c1, c2) -> Double.compare(keyExtractor.applyAsDouble(c1), keyExtractor.applyAsDouble(c2));
    }
}

排序List

package lambda.bean;

/**
 * @author wangkaijie
 */
public class Student implements Comparable<Student> {
    private int id;
    private String name;
    private int age;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public int getId() {
        return id;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    @Override
    public int compareTo(Student ob) {
        return name.compareTo(ob.getName());
    }
    @Override
    public boolean equals(final Object obj) {
        if (obj == null) {
            return false;
        }
        final Student std = (Student) obj;
        if (this == std) {
            return true;
        } else {
            return (this.name.equals(std.name) && (this.age == std.age));
        }
    }
    @Override
    public int hashCode() {
        int hashno = 7;
        hashno = 13 * hashno + (name == null ? 0 : name.hashCode());
        return hashno;
    }
}

package lambda.bean;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
import  static java.util.stream.Collectors.toList;
/**
 * @author wangkaijie
 * @date 2018/1/28
 */
public class SortList {
    public static void main(String arg[]) {
        List<Student> list = new ArrayList<Student>();
        list.add(new Student(1, "Mahesh", 12));
        list.add(new Student(2, "Suresh", 15));
        list.add(new Student(3, "Nilesh", 10));

        System.out.println("---以名字的天然順序排序---");
        List<Student> slist = list.stream().sorted().collect(toList());
        slist.forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

        System.out.println("---以名字的天然順序的反序排序---");
        slist = list.stream().sorted(Comparator.reverseOrder()).collect(toList());
        slist.forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

        System.out.println("---經過age排序---");
        slist = list.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList());
        slist.forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

        System.out.println("---經過age的逆序---");
        slist = list.stream().sorted(Comparator.comparing(Student::getAge).reversed()).collect(Collectors.toList());
        slist.forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));
    }
}

Stream類型的sorted方法有兩個版本：

//按照目標對象的天然排序(Natural Order)方式進行排序,且目標對象類型必須實現Comparable接口
Stream<T> sorted();
//傳入一個函數式接口
Stream<T> sorted(Comparator<? super T> comparator);

sorted方法返回的仍然是一個Stream對象。