Java中Arrays的sort方法

数组的排序，Java自带的Arrays类的sort方法主要内容包括插入排序结合分治排序两种排序算法在里面。

先分别介绍一下两种排序方式：

第一种：通过分治法实现的并归排序。

@SuppressWarnings("unchecked" )        public static void mergeSort(Comparable[] src , Comparable[] dest, int low, int high) {              if (high - low == 1) {                    return;             }              if (high - low == 2) {                    if (dest[low].compareTo(dest[high - 1]) > 0) {                          swap(dest, low, high - 1);                   }                    return;             }              int mid = (low+high) >> 1;              mergeSort(dest, src , low, mid);              mergeSort(dest, src , mid, high);              for (int i = low, p = low, q = mid; i < high; i++) {                    if (q == high|| (p != mid &&  src [p].compareTo(src[q]) < 0)) {                         dest[i] = src[p++];                   } else {                         dest[i] = src[q++];                   }             }       }

第二种：插入排序。

private static void InsertionSort(Comparable[] src,Comparable[] dest,int low,int high){              for(int i=low;i<high;i++){                    for(int j=i;j>low;j--){                          if(dest[j].compareTo(dest[j-1])<0){                                swap(dest, j, j-1);                         }                   }             }       }

还有一个工具方法

private static void swap(Object[] x, int a, int b) {             Object t = x[a];             x[a] = x[b];             x[b] = t;       }

整个Java类的内容如下：

public class ArraysSort {        @SuppressWarnings("unchecked" )        public static void mergeSort(Comparable[] src, Comparable[] dest, int low, int high) {              if (high - low == 1) {                    return;             }              if (high - low == 2) {                    if (dest[low].compareTo(dest[high - 1]) > 0) {                          swap(dest, low, high - 1);                   }                    return;             }              int mid = (low+high) >> 1;              mergeSort(dest, src, low, mid);              mergeSort(dest, src, mid, high);              for (int i = low, p = low, q = mid; i < high; i++) {                    if (q == high|| (p != mid &&  src[p].compareTo(src[q]) < 0)) {                         dest[i] = src[p++];                   } else {                         dest[i] = src[q++];                   }             }       }        @SuppressWarnings({ "unused" , "unchecked" })        private static void InsertionSort(Comparable[] src, Comparable[] dest,int low, int high) {              for (int i = low; i < high; i++) {                    for (int j = i; j > low; j--) {                          if (dest[j].compareTo(dest[j - 1]) < 0) {                                swap(dest, j, j - 1);                         }                   }             }       }        private static String[] getStrings(int length) {             Random random = new Random();             String[] strs = new String[length];              for (int i = 0; i < length; i++) {                    int temp = random.nextInt(999);                   strs[i] = Integer. toString(temp);             }              return strs;       }        private static void swap (Object[] x, int a, int b) {             Object t = x[a];             x[a] = x[b];             x[b] = t;       }        public static void main(String[] args) {             String[] strs = getStrings(10);             String[] aux = strs.clone();              long begin = System.currentTimeMillis();              mergeSort(strs, aux, 0, strs.length);             System. out.println(System.currentTimeMillis() - begin);             System. out.println(Arrays.asList(strs));             System. out.println(Arrays.asList(aux));       } }

将插入排序放入并归排序中：

public class ArraysSort {        /**        * 排序的代码        * @param src        * @param dest        * @param low        * @param high        */        @SuppressWarnings("unchecked" )        public static void mergeSort(Comparable[] src, Comparable[] dest, int low, int high) {              if (high - low < 7) {                    for (int i = low; i < high; i++) {                          for (int j = i; j > low; j--) {                                if (dest[j].compareTo(dest[j - 1]) < 0) {                                      swap(dest, j, j - 1);                               }                         }                   }                    return;             }              int mid = (low+high) >> 1;              mergeSort(dest, src, low, mid);              mergeSort(dest, src, mid, high);              for (int i = low, p = low, q = mid; i < high; i++) {                    if (q == high|| (p != mid &&  src[p].compareTo(src[q]) < 0)) {                         dest[i] = src[p++];                   } else {                         dest[i] = src[q++];                   }             }       }        /**        * 数组置换位置        * @param x        * @param a        * @param b        */        private static void swap(Object[] x, int a, int b) {             Object t = x[a];             x[a] = x[b];             x[b] = t;       }        /**        * 测试的方法        * @param length        * @return        */        private static String[] getStrings(int length) {             Random random = new Random();             String[] strs = new String[length];              for (int i = 0; i < length; i++) {                    int temp = random.nextInt(999);                   strs[i] = Integer. toString(temp);             }              return strs;       }        public static void main(String[] args) {             String[] strs = getStrings(10);             String[] aux = strs.clone();              long begin = System.currentTimeMillis();              mergeSort(strs, aux, 0, strs.length);             System. out.println(System.currentTimeMillis() - begin);             System. out.println(Arrays.asList(strs));             System. out.println(Arrays.asList(aux));       } }

Arrays的sort方法如下：

private static void mergeSort(Object[] src, Object[] dest, int low, int high, int off) {        int length = high - low;        // Insertion sort on smallest arrays         if (length < INSERTIONSORT_THRESHOLD) {             for (int i=low; i<high; i++)                 for (int j=i; j>low &&                    (( Comparable) dest[j-1]).compareTo(dest[j])>0; j--)                     swap(dest, j, j-1);             return;         }         // Recursively sort halves of dest into src         int destLow  = low;         int destHigh = high;         low  += off;         high += off;         int mid = (low + high) >> 1;         mergeSort(dest, src, low, mid, -off) ;         mergeSort(dest, src, mid, high, -off) ;         // If list is already sorted, just copy from src to dest.  This is an         // optimization that results in faster sorts for nearly ordered lists.         if (((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {             System. arraycopy(src, low, dest, destLow, length);             return;         }         // Merge sorted halves (now in src) into dest         for(int i = destLow, p = low, q = mid; i < destHigh; i++) {             if (q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)                 dest[i] = src[p++];             else                 dest[i] = src[q++];         }     }     /**      * Swaps x[a] with x[b].      */     private static void swap(Object[] x, int a, int b) {       Object t = x[a];       x[a] = x[b];       x[b] = t;     }