Collections,sort()实现原理

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查看源码可以发现Collections.sort的实现是Arrays.sort，而Arrays.sort的实现是ComparableTimSort.sort,然后才到sort方法和它的定义，查看排序的主体部分也可以发现一个binarySort的方法，这是排序方法的实现，是通过调用Object的CompareTo进行比较的。

每一步代码如下：

public class ListSort {    public static void main(String[] args){        List<String> list=new ArrayList<String>();        list.add("ohjx");        list.add("ghjg");        list.add("hggh");        Collections.sort(list);        for (String listString:list){            System.out.println(listString);        }    }}

Arrays.sort：

public static <T extends Comparable<? super T>> void sort(List<T> list) {    Object[] a = list.toArray();    Arrays.sort(a);    ListIterator<T> i = list.listIterator();    for (int j=0; j<a.length; j++) {        i.next();        i.set((T)a[j]);    }}

ComparableTimSort.sort：

public static void sort(Object[] a) {    if (LegacyMergeSort.userRequested)        legacyMergeSort(a);    else        ComparableTimSort.sort(a);}

sort：

static void sort(Object[] a) {      sort(a, 0, a.length);}static void sort(Object[] a, int lo, int hi) {    rangeCheck(a.length, lo, hi);    int nRemaining  = hi - lo;    if (nRemaining < 2)        return;  // Arrays of size 0 and 1 are always sorted    // If array is small, do a "mini-TimSort" with no merges    if (nRemaining < MIN_MERGE) {        int initRunLen = countRunAndMakeAscending(a, lo, hi);        binarySort(a, lo, hi, lo + initRunLen);        return;    }

binarySort：

private static void binarySort(Object[] a, int lo, int hi, int start) {    assert lo <= start && start <= hi;    if (start == lo)        start++;    for ( ; start < hi; start++) {        @SuppressWarnings("unchecked")        Comparable<Object> pivot = (Comparable) a[start];        // Set left (and right) to the index where a[start] (pivot) belongs        int left = lo;        int right = start;        assert left <= right;        /*         * Invariants:         *   pivot >= all in [lo, left).         *   pivot <  all in [right, start).         */        while (left < right) {            int mid = (left + right) >>> 1;            if (pivot.compareTo(a[mid]) < 0)                right = mid;            else                left = mid + 1;        }        assert left == right;        /*         * The invariants still hold: pivot >= all in [lo, left) and         * pivot < all in [left, start), so pivot belongs at left.  Note         * that if there are elements equal to pivot, left points to the         * first slot after them -- that's why this sort is stable.         * Slide elements over to make room for pivot.         */        int n = start - left;  // The number of elements to move        // Switch is just an optimization for arraycopy in default case        switch (n) {            case 2:  a[left + 2] = a[left + 1];            case 1:  a[left + 1] = a[left];                     break;            default: System.arraycopy(a, left, a, left + 1, n);        }        a[left] = pivot;    }}

这就是层层调用的代码（按顺序）

Collections.sort方法如果只有一个参数，那么默认采用自然排序的方法对指定的列表（参数）进行排序，也可以传入两个参数，一个是待排序的列表，另一个就是指定的排序规则。两个方法的定义如下：

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