java数组排序Arrays.sort，以及Comparator接口的用法

有的时候需要对数组里的element进行排序。当然可以自己编写合适的排序方法，但既然java包里有自带的Arrays.sort排序方法，在数组元素比较少的时候为何不用？

Sorting an Array1. 数字排序 int[] intArray = new int[] {4, 1, 3, -23};

Arrays.sort(intArray);

输出： [-23, 1, 3, 4]

2. 字符串排序，先大写后小写 String[] strArray = new String[] {"z", "a", "C"};

Arrays.sort(strArray);

输出： [C, a, z]

3. 严格按字母表顺序排序，也就是忽略大小写排序 Case-insensitive sort

Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);

输出： [a, C, z]

4. 反向排序， Reverse-order sort

Arrays.sort(strArray, Collections.reverseOrder());

输出：[z, a, C]

5. 忽略大小写反向排序 Case-insensitive reverse-order sort

Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);

Collections.reverse(Arrays.asList(strArray));

输出： [z, C, a]

java初学者最常见的错误思想，就是试图去写一些方法来完成数组的排序功能，其实，数组排序功能，在java的api里面早已实现，我们没有必要去重复制造轮子。

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。

package demo1.client;

import java.util.Arrays;

import java.util.Comparator;

public class ArraySortDemo {



public voidsortIntArray() {

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]);

//调用数组的静态排序方法sort

Arrays.sort(arrayToSort);

System.out.println("排序后");

for
(int i =0; i < arrayToSort.length; i++)

System.out.println(arrayToSort[i]);

}



public voidsortStringArray() {

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");

//调用数组的静态排序方法sort

Arrays.sort(arrayToSort);

for
(int i =0; i < arrayToSort.length; i++)

System.out.println(arrayToSort[i]);

}



public voidsortObjectArray() {

Dog
o1 = newDog("dog1", 1);

Dog
o2 = newDog("dog2", 4);

Dog
o3 = newDog("dog3", 5);

Dog
o4 = newDog("dog4", 2);

Dog
o5 = newDog("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());

}

}

publicstatic void main(String[] args) {

ArraySortDemo
t = new ArraySortDemo();

t.sortIntArray();

t.sortStringArray();

t.sortObjectArray();

}

}

class Dog {

privateString name;

private intweight;

publicDog(String name, int weight) {

this.setName(name);

this.weight=
weight;

}

public intgetWeight() {

returnweight;

}

public voidsetWeight(int weight) {

this.weight=
weight;

}

public voidsetName(String name) {

this.name
=name;

}

publicString getName() {

returnname;

}

}

class ByWeightComparator implements Comparator {

public finalint compare(Object pFirst, Object pSecond) {

intaFirstWeight
= ((Dog) pFirst).getWeight();

intaSecondWeight
= ((Dog) pSecond).getWeight();

int
diff =aFirstWeight - aSecondWeight;

if (diff>
0)


return1;

if (diff<
0)


return-1;

else


return0;

}

}