数组排序Arrays.sort

原文：http://hi.baidu.com/dobodo/blog/item/53d5c990b1ed2885a877a4a8.html

 

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 test;

import java.util.Arrays;
import java.util.Comparator;

public class ArraySortDemo {
/**
* 整数型数组排序
*/
public void sortIntArray() {
   int[] arrayToSort = new int[] { 48, 5, 89, 80, 81, 23, 45, 16, 2 };
   System.out.println("整数型数组排序,排序前:");
   for (int i = 0; i < arrayToSort.length; i++){
    System.out.print(arrayToSort[i]+",");
   }
   // 调用数组的静态排序方法sort
  Arrays.sort (arrayToSort);
   System.out.println();
   System.out.println("排序后:");
   for (int i = 0; i < arrayToSort.length; i++){
    System.out.print(arrayToSort[i]+",");
   }
}

/**
* 字符型数组排序demo
*/
public void sortStringArray() {
   String[] arrayToSort = new String[] { "Oscar", "Charlie", "Ryan",
     "Adam", "David","aff","Aff" };
   System.out.println();
   System.out.println("字符型数组排序,排序前:");
   for (int i = 0; i < arrayToSort.length; i++){
    System.out.print(arrayToSort[i]+",");
   }
   System.out.println();
   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.print(arrayToSort[i]+",");
   }
}

/**
* 对象数组排序demo
*/
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();
   System.out.println("对象数组排序排序前:");
   for (int i = 0; i < dogs.length; i++) {
    Dog dog = dogs[i];
    System.out.print(dog.getName()+"["+dog.getWeight()+"],");
   }
   Arrays.sort(dogs, new ByWeightComparator());
   System.out.println();
   System.out.println("排序后：");
   for (int i = 0; i < dogs.length; i++) {
    Dog dog = dogs[i];
    System.out.print(dog.getName()+"["+dog.getWeight()+"],");
   }
}

public static void main(String[] args) {
   ArraySortDemo t = new ArraySortDemo();
   t.sortIntArray();
   t.sortStringArray();
   t.sortObjectArray();
}
}

/**
* 定义了一个Dog类
*/
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;
}
}

/**
* 因为要对对象进行排序，所以要实现java.util.Comparator接口的compare(T o1, T o2)方法，在该方法中自定义排序算法。
*/
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;
}
}

运行结果：

整数型数组排序,排序前:
48,5,89,80,81,23,45,16,2,
排序后:
2,5,16,23,45,48,80,81,89,
字符型数组排序,排序前:
Oscar,Charlie,Ryan,Adam,David,aff,Aff,
排序后:
Adam,Aff,Charlie,David,Oscar,Ryan,aff,
对象数组排序排序前:
dog1[1],dog2[4],dog3[5],dog4[2],dog5[3],
排序后：
dog1[1],dog4[2],dog5[3],dog2[4],dog3[5],