有的時候需要對數組里的element進行排序。當然可以自己編寫合適的排序方法，但既然java包里有自帶的Arrays.sort排序方法，在數組元素比較少的時候為何不用？

Sorting an Array 1. 數字排序? int[] intArray = new int[] { 4, 1, 3, -23 };
Arrays.sort(intArray);
輸出： [-23, 1, 3, 4]
 2. 字符串排序，先大寫后小寫 String[] strArray = new String[] { "z", "a", "C" };
Arrays.sort(strArray);
輸出： [C, a, z]
 3. 嚴格按字母表順序排序，也就是忽略大小寫排序 Case-insensitive sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
輸出： [a, C, z]
4. 反向排序， Reverse-order sort
Arrays.sort(strArray, Collections.reverseOrder());
輸出：[z, a, C]
5. 忽略大小寫反向排序 Case-insensitive reverse-order sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(Arrays.asList(strArray));
輸出： [z, C, a]

java初學者最常見的錯誤思想，就是試圖去寫一些方法來完成數組的排序功能，其實，數組排序功能，在java的api里面早已實現，我們沒有必要去重復制造輪子。
Arrays類有一個靜態方法sort,利用這個方法我們可以傳入我們要排序的數組進去排序，因為我們傳入的是一個數組的引用，所以排序完成的結果也通過這個引用的來更改數組.對于整數、字符串排序，jdk提供了默認的實現，如果要對一個對象數組排序，則要自己實現java.util.Comparator接口。

package demo1.client;
import java.util.Arrays;
import java.util.Comparator;

public class ArraySortDemo {
???
??? public void sortIntArray() {
??? ??? int[] arrayToSort = new int[] { 48, 5, 89, 80, 81, 23, 45, 16, 2 };
??? ??? System.out.println("排序前");
??? ??? for (int i = 0; i < arrayToSort.length; i++)
??? ??? ??? System.out.println(arrayToSort[i]);
??? ??? // 調用數組的靜態排序方法sort
??? ??? Arrays.sort(arrayToSort);
??? ??? System.out.println("排序后");
??? ??? for (int i = 0; i < arrayToSort.length; i++)
??? ??? ??? System.out.println(arrayToSort[i]);
??? }

???
??? public void sortStringArray() {
??? ??? String[] arrayToSort = new String[] { "Oscar", "Charlie", "Ryan",
??? ??? ??? ??? "Adam", "David" };
??? ??? System.out.println("排序前");
??? ??? for (int i = 0; i < arrayToSort.length; i++)
??? ??? ??? System.out.println(arrayToSort[i]);
??? ??? System.out.println("排序后");
??? ??? //調用數組的靜態排序方法sort
??? ??? Arrays.sort(arrayToSort);

??? ??? for (int i = 0; i < arrayToSort.length; i++)
??? ??? ??? System.out.println(arrayToSort[i]);
??? }

???
??? public void sortObjectArray() {
??? ??? Dog o1 = new Dog("dog1", 1);
??? ??? Dog o2 = new Dog("dog2", 4);
??? ??? Dog o3 = new Dog("dog3", 5);
??? ??? Dog o4 = new Dog("dog4", 2);
??? ??? Dog o5 = new Dog("dog5", 3);
??? ??? Dog[] dogs = new Dog[] { o1, o2, o3, o4, o5 };
??? ??? System.out.println("排序前");
??? ??? for (int i = 0; i < dogs.length; i++) {
??? ??? ??? Dog dog = dogs[i];
??? ??? ??? System.out.println(dog.getName());
??? ??? }
??? ??? Arrays.sort(dogs, new ByWeightComparator());
??? ??? System.out.println("排序后：");
??? ??? for (int i = 0; i < dogs.length; i++) {
??? ??? ??? Dog dog = dogs[i];
??? ??? ??? System.out.println(dog.getName());
??? ??? }
??? }
??? public static void main(String[] args) {
??? ??? ArraySortDemo t = new ArraySortDemo();
??? ??? t.sortIntArray();
??? ??? t.sortStringArray();
??? ??? t.sortObjectArray();
??? }
}


class Dog {
??? private String name;
??? private int weight;

??? public Dog(String name, int weight) {
??? ??? this.setName(name);
??? ??? this.weight = weight;
??? }

??? public int getWeight() {
??? ??? return weight;
??? }

??? public void setWeight(int weight) {
??? ??? this.weight = weight;
??? }

??? public void setName(String name) {
??? ??? this.name = name;
??? }

??? public String getName() {
??? ??? return name;
??? }
}

class ByWeightComparator implements Comparator {
??? public final int compare(Object pFirst, Object pSecond) {
??? ??? int aFirstWeight = ((Dog) pFirst).getWeight();
??? ??? int aSecondWeight = ((Dog) pSecond).getWeight();
??? ??? int diff = aFirstWeight - aSecondWeight;
??? ??? if (diff > 0)
??? ??? ??? return 1;
??? ??? if (diff < 0)
??? ??? ??? return -1;
??? ??? else
??? ??? ??? return 0;
??? }
}