Java数组排序Arrays.sort,以及Comparator接口的用法

时间:2022-01-09 02:50:52

http://blog.csdn.net/wang_yubin/article/details/8059332


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 Array

      1. 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*。

  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 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]);

  // 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 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");

  //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 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;

  }

  }