Java中比较器Comparable和Comparator超详细解析

class Person implements Comparable<Person> {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public int compareTo(Person other) {
        return Integer.compare(this.age, other.age); // 按年龄升序
    }

    @Override
    public String toString() {
        return name + " (" + age + ")";
    }
}

public class ComparableExample {
    public static void main(String[] args) {
        Person[] people = {
            new Person("Alice", 25),
            new Person("Bob", 22),
            new Person("Charlie", 30)
        };

        Arrays.sort(people); // 按 `Comparable` 规则排序
        System.out.println(Arrays.toString(people));
    }
}

class NameComparator implements Comparator<Person> {
    @Override
    public int compare(Person p1, Person p2) {
        return p1.name.compareTo(p2.name); // 按名称字母升序
    }
}

public class ComparatorExample {
    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 25));
        people.add(new Person("Bob", 22));
        people.add(new Person("Charlie", 30));

        people.sort(new NameComparator()); // 使用外部比较器进行排序
        System.out.println(people);
    }
}

@Override
public int compareTo(Person other) {
    return Integer.compare(other.age, this.age); // 降序排序
}

Comparator<Person> ageAscending = Comparator.comparingInt(p -> p.age); // 按年龄升序
Comparator<Person> ageDescending = (p1, p2) -> Integer.compare(p2.age, p1.age); // 按年龄降序

public static void sort(int[] a) {
    DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
}

static void sort(int[] a, int left, int right, int[] work, int workBase, int workLen) {
    if (right - left < QUICKSORT_THRESHOLD) {
        insertionSort(a, left, right); // 小数组使用插入排序
        return;
    }

    int pivot1 = a[left], pivot2 = a[right];
    if (pivot1 > pivot2) {
        swap(a, left, right);
        pivot1 = a[left];
        pivot2 = a[right];
    }

    int less = left + 1;
    int great = right - 1;

    for (int k = less; k <= great; k++) {
        if (a[k] < pivot1) {
            swap(a, k, less++);
        } else if (a[k] > pivot2) {
            swap(a, k, great--);
        }
    }

    sort(a, left, less - 1, work, workBase, workLen);
    sort(a, less, great, work, workBase, workLen);
    sort(a, great + 1, right, work, workBase, workLen);
}

public static <T> void sort(T[] a, Comparator<? super T> c) {
    if (c == null) {
        Arrays.sort(a); // 调用默认的 Comparable 方式排序
    } else {
        TimSort.sort(a, c); // 使用 Comparator 进行排序
    }
}

static <T> void sort(T[] a, Comparator<? super T> c) {
    int lo = 0, hi = a.length;
    if (hi - lo < INSERTION_SORT_THRESHOLD) {
        insertionSort(a, lo, hi, c); // 小数据量使用插入排序
        return;
    }
    int mid = (lo + hi) >>> 1;
    sort(a, lo, mid, c);
    sort(a, mid, hi, c);
    merge(a, lo, mid, hi, c); // 归并两个有序数组
}

public static <T extends Comparable<? super T>> void sort(List<T> list) {
    Object[] array = list.toArray();
    Arrays.sort(array);
    for (int i = 0; i < list.size(); i++)
        list.set(i, (T) array[i]);
}