【Java】Comparable & Comparator 自定义排序
自定义排序两种方式
- 实现Comparable接口，并重写compareTo方法
- 实现Comparator接口，并重写compare方法
Collections工具类
sort方法
- sort（List
） - sort(List
, comparator )
自己实现一个Collections类（MySort）
package compare;
import java.sql.Date;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
/**
* 排序实现,对数组
* @author 袁盛桐
*
*/
public class MySort {
/**
* 数组排序+comparator接口
* @param
*/
public static void sort(String[] arr, MyComparator com) {
boolean sorted = true;
int len = arr.length;
//趟数
for(int j =0; j < len-1; j++) {
//假定有序
sorted = true;
for(int i =0; i> void sort(List arr) {
//第一步：转成数组
Object[] arr2 = arr.toArray();
sort(arr2);
//第二部：改变容器中对应的值
for(int i =0; i> void sort(T[] arr) {
boolean sorted = true;
int len = arr.length;
//趟数
for(int j =0; j < len-1; j++) {
//假定有序
sorted = true;
for(int i =0; i list = new ArrayList();
list.add("a");
list.add("abcd");
list.add("abc");
list.add("def");
MySort.sort(list);
System.out.println(list);
System.out.println("使用comparator排序");
String[] arr3 = new String[] {"a","abcd","abc","def"};
MySort.sort(arr3,new MyComparator());
for(String x:arr3) {
System.out.println(x);
}
}
}
自定义类Newsletter测试，并用Comparable接口实现自定义排序功能
定义一个NewsletterSort类，并重写compareTo方法，在main中, 直接调用collections类中的sort方法，并传入list
package compare;
import java.sql.Date;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* 实现接口comparable方式排序
* @author 袁盛桐
*
*/
public class NewsletterSort implements java.lang.Comparable{
//标题
private String title;
//点击量
private int hits;
//时间
private Date Pubtime;
public NewsletterSort() {
}
public NewsletterSort(String title, int hits, Date pubtime) {
super();
this.title = title;
this.hits = hits;
Pubtime = pubtime;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public int getHits() {
return hits;
}
public void setHits(int hits) {
this.hits = hits;
}
public Date getPubtime() {
return Pubtime;
}
public void setPubtime(Date pubtime) {
Pubtime = pubtime;
}
//按时间降序+点击量升序+标题降序业务逻辑
@Override
public int compareTo(NewsletterSort o) {
int result= 0;
//比较时间降序
result = -this.Pubtime.compareTo(o.Pubtime);
if(result == 0) {//时间相同
//看点击量
result = this.hits-o.hits;
if(result == 0) {//点击量相同
//标题
result = -this.title.compareTo(o.title);
}
}
return result;
}
//重写tostring方法
@Override
public String toString() {
StringBuilder x = new StringBuilder();
x.append("标题：").append(this.title);
x.append(",时间：").append(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(this.Pubtime));
x.append(",点击量：").append(this.hits).append("\n");
return x.toString();
}
public static void main(String[] args) {
List news = new ArrayList();
news.add(new NewsletterSort("标题长度为111111111111111",100, new Date(System.currentTimeMillis()-5000*60*60)));
news.add(new NewsletterSort("标题长度为222222222222",50, new Date(System.currentTimeMillis()-1000*60*60)));
news.add(new NewsletterSort("标题长度为3333333",30, new Date(System.currentTimeMillis()-1000*60*60)));
System.out.println("排序前"+news);
MySort mySort = new MySort();
mySort.sort(news);
System.out.println("排序后"+news);
}
}
自定义类Goods测试，并用Comparator接口实现自定义排序功能
自定义GoodsSort类，自定义根据自己业务逻辑实现的排序类，实现comparator接口中的compare方法
与comparable方法不同的是，在调用collections.sort方法时，除了传入list
package Goods_comparator;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class GoodsSort {
//商品名
private String name;
//价格
private double price;
//收藏量
private double favorate;
public GoodsSort() {
}
public GoodsSort(String name, double price, double favorate) {
super();
this.name = name;
this.price = price;
this.favorate = favorate;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public double getFavorate() {
return favorate;
}
public void setFavorate(double favorate) {
this.favorate = favorate;
}
@Override
public String toString() {
return "商品名:"+name+",收藏量:"+favorate+",价格:"+price+"\n";
}
public static void main(String[] args) {
List list = new ArrayList();
list.add(new GoodsSort("goodslong111111111",100,2000));
list.add(new GoodsSort("goodsmiddle2222",300,1000));
list.add(new GoodsSort("goodsshort333",50,7000));
System.out.println("排序前"+list);
//传入list和排序类,排序类实现comparator接口，实现解耦的目的
Collections.sort(list, new GoodsPriceCompare());
System.out.println("排序后"+list);
}
}
package Goods_comparator;
/**
* 对Goods按价格降序排序的业务类
* 实现comparator接口方式排序
* @author 袁盛桐
*
*/
public class GoodsPriceCompare implements java.util.Comparator {
@Override
public int compare(GoodsSort o1, GoodsSort o2) {
return -(o1.getPrice()-o2.getPrice()>0?1:(o1.getPrice()==o2.getPrice()?0:-1));
}
}