模版方法模式--java数组排序及Comparable接口用法

1、概述

???? Arrays类有一个静态方法sort,利用这个方法我们可以传入我们要排序的数组进去排序，因为我们传入的是一个数组的引用，所以排序完成的结果也通过这个引用的来更改数组。对于整数、字符串排序，jdk提供了默认的实现，如果要对一个对象数组排序，则要自己实现java.util.Comparator接口。

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java.util.Arrays中代码

public static void sort(Object[] a) {        Object[] aux = (Object[])a.clone();        mergeSort(aux, a, 0, a.length, 0);}

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++];        }    }

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

?冒泡排序法

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2、例子（鸭子大小比较）

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Duck需要实现Comparable

public class Duck implements Comparable {String name;int weight;public Duck(String name, int weight) {this.name = name;this.weight = weight;}public String toString() {return name + " weights " + weight;}@Overridepublic int compareTo(Object o) {Duck otherDuck = (Duck) o;if (this.weight < otherDuck.weight)return -1;else if (this.weight == otherDuck.weight)return 0;elsereturn 1;}}

public class DackSortTestDrive {public static void main(String[] args) {Duck[] ducks = {new Duck("Daffy", 8),new Duck("Dewey", 2),new Duck("Howard", 7),new Duck("Louie", 2),new Duck("Donald", 10),new Duck("Huey", 3)};System.out.println("Before sorting:");display(ducks);Arrays.sort(ducks);System.out.println("\nAfter sorting:");display(ducks);}public static void display(Duck[] ducks){for (int i = 0; i < ducks.length; i++) {System.out.println(ducks[i]);}}}

?结果：

Before sorting:
Daffy weights 8
Dewey weights 2
Howard weights 7
Louie weights 2
Donald weights 10
Huey weights 3

After sorting:
Dewey weights 2
Louie weights 2
Huey weights 3
Howard weights 7
Daffy weights 8
Donald weights 10

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3、总结

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Arrays.sort方法控制算法，sort()依赖一个Comparable类提供compareTo()的实现。

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for(int i=low;i<high;i++){        ...compareTo()...        ...swap()...}

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