面向接口编程
Comparable接口中只有一个方法
public int compareTo(Object obj)返回0：this==obj
返回正数：this>obj
返回负数：this<obj
实现Comparable接口的类通过实现compareTo方法确定该类对象的排序方式;
独立于实体类，便于应对各种排序规则;
package com.alexanderli95.innerType;
import java.util.Date;
/**
* 内置引用数据类型的比较（常用的）
*/
public class Demo01 {
public static void main(String[] args) {
/**
*根据基本数据类型比较
*return (x < y) ? -1 : ((x == y) ? 0 : 1);
*/
Integer i;
/**
* 根据Unicode编码比较
* return x - y;
*/
Character c;
/**
* public int compareTo(String anotherString) {
* int len1 = value.length;
* int len2 = anotherString.value.length;
* int lim = Math.min(len1, len2);
* char v1[] = value;
* char v2[] = anotherString.value;
*
* int k = 0;
* while (k < lim) {
* char c1 = v1[k];
* char c2 = v2[k];
* if (c1 != c2) {
* return c1 - c2;
* }
* k++;
* }
* return len1 - len2;
* }
*
* 如果前一个是另一个起始部分的字串，返回长度之差；否则返回第一个不相等的字符的Unicode编码差
*/
String str;
//根据日期的长整形数比较
Date date;
}
}工具类Utils的实现：
package com.alexanderli95.innerType;
import java.util.List;
/**
* 自己实现一个工具类（排序）
*/
public class Utils {
//数组降序排序
public static void sort(Object[] data){
boolean sorted=true;
int times=data.length;
//冒泡排序
for(int j=0;j<data.length;j++) {
sorted=true;
for (int i = 0; i < times-1; i++) {
if (((Comparable)data[i]).compareTo(data[i + 1])>0) {
Object temp = data[i];
data[i] = data[i + 1];
data[i + 1] = temp;
sorted=false;
}
}
if(sorted){
break;
}
times--;
}
}
//使用泛型方法
public static <T extends Comparable>void sort(T[] data){
boolean sorted=true;
int times=data.length;
//冒泡排序
for(int j=0;j<data.length;j++) {
sorted=true;
for (int i = 0; i < times-1; i++) {
if (((Comparable)data[i]).compareTo(data[i + 1])>0) {
T temp = data[i];
data[i] = data[i + 1];
data[i + 1] = temp;
sorted=false;
}
}
if(sorted){
break;
}
times--;
}
}
//容器排序
public static <T extends Comparable> void sort(List<T> array){
Object[] data=array.toArray();
sort(data);
for(int i=0;i<data.length;i++){
array.set(i,(T)data[i]);
}
}
}JDK 自带的Collections类
package com.alexanderli95.innerType;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* Collection
*/
public class Demo05 {
public static void main(String[] args) {
List<String> list=new ArrayList<String>();
String[] strings={"a","asd","as","asdfg","wwww"};
for(int i=0;i<strings.length;i++){
list.add(strings[i]);
}
//调用了重写的compare方法
Collections.sort(list,new StringComp()); //public static <T> void sort(List<T> list, Comparator<? super T> c)
System.out.println(list);
System.out.println("================================");
//调用默认compare方法
List<String> list2=new ArrayList<String>();
String[] strings2={"a","asd","as","asdfg","wwww"};
for(int i=0;i<strings2.length;i++){
list2.add(strings2[i]);
}
Collections.sort(list2);
System.out.println(list2);
}
}实现compareTo()方法，实现新闻类的排序：
1.NewsItem.java
package com.alexanderli95.innerType;
import java.text.SimpleDateFormat;
import java.util.Date;
public class NewsItem implements java.lang.Comparable<NewsItem> {
private String title; //标题
private int hint; //点击量
private Date publishTime; //发布时间
public NewsItem(String title, int hint, Date publishTime) {
this.title = title;
this.hint = hint;
this.publishTime = publishTime;
}
public NewsItem() {
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public int getHint() {
return hint;
}
public void setHint(int hint) {
this.hint = hint;
}
public Date getPublishTime() {
return publishTime;
}
public void setPublishTime(Date publishTime) {
this.publishTime = publishTime;
}
//时间降序+点击量降序+标题降序
@Override
public int compareTo(NewsItem o) {
int result=0;
result=-this.publishTime.compareTo(o.publishTime);
if(0==result){ //时间相同
//比较点击量
result=-(this.hint-o.hint);
if(0==result){ //点击量相同
//比较标题
result=-this.title.compareTo(o.title);
}
}
return result;
}
@Override
public String toString() {
StringBuilder sb=new StringBuilder();
sb.append("标题：").append(this.title);
sb.append(" 点击量：").append(this.hint);
sb.append(" 发布日期：").append(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(this.publishTime));
sb.append("\n");
return sb.toString();
}
}2.NewsItemApp.java
package com.alexanderli95.innerType;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Date;
import java.util.List;
public class NewsItemApp {
public static void main(String[] args) {
List<NewsItem> news=new ArrayList<NewsItem>();
news.add(new NewsItem("行业改革",100,new Date(System.currentTimeMillis())));
news.add(new NewsItem("社保",90,new Date(System.currentTimeMillis()-60*60*1000)));
news.add(new NewsItem("医疗",900,new Date(System.currentTimeMillis())));
Collections.sort(news); //sort会自动调用compareTo()方法
System.out.println(news);
}
}商品类的排序：
==思想==：Goods类只作为一个JavaBean(解耦：与实体类分离，保证实体类的独立性和完整性)，额外增加GoodsPriceComp类用于按照价格进行排序，优势在于：如果需要通过其他属性进行排序，不需要改变原来的代码，只需要增加新的类即可(方便：可以方便的应对多变的排序规则)；
1.Goods.java
package com.alexanderli95.innerType;
public class Goods {
private String name;
private int fav;
private double price;
@Override
public String toString() {
return "商品名："+this.name+" 收藏量："+this.fav+" 价格："+this.price+"\n";
}
public Goods(String name, int fav, double price) {
this.name = name;
this.fav = fav;
this.price = price;
}
public Goods() {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getFav() {
return fav;
}
public void setFav(int fav) {
this.fav = fav;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}2.GoodsPriceComp.java
package com.alexanderli95.innerType;
public class GoodsPriceComp implements java.util.Comparator<Goods>{
//比较价格（降序）
@Override
public int compare(Goods o1, Goods o2) {
return -(o1.getPrice()-o2.getPrice()>0?1:(o1.getPrice()==o2.getPrice()?0:-1));
}
}3.GoodsApp.java
package com.alexanderli95.innerType;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class GoodsApp {
public static void main(String[] args) {
List<Goods> goods=new ArrayList<Goods>();
goods.add(new Goods("iphone 8",100,8000));
goods.add(new Goods("Samsung x",60,6000));
goods.add(new Goods("Mi 9",500,7999));
Collections.sort(goods,new GoodsPriceComp()); //sort会自动调用GoodsPriceComp中的compare()方法
System.out.println(goods);
}
}