Java 之集合排序

青旅半醒 2022-09-27 06:35 169阅读 0赞

*  排序
 *  Comparable接口
 *  Comparator接口 排序器
 *  通用排序器

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## 1. 排序 ##

我们都知道，算法有各种各样的算法。排序算法通常使用的主要有九种。但是，我们排序的时候，如果自己实现算法的话就会非常麻烦，那么我们在工业界的代码应该如何书写的？Java内主要提供了Comparable接口和Comparator 接口。

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## 2. Comparable接口 ##

主要需要门重写Model对象中的compareTo(Object o)类。  
举例说明如下所示:

package test;
    
    import java.util.Comparator;
    /** * 具体的比较类（比较器），实现Comparator接口 * @author breeze * */
    public class ComparatorConsunInfo implements Comparator<ConsumInfo> {
        /** * 顺序（从小到大）： * if(price < o.price){ return -1; } if(price > o.price){ return 1; } * 倒序（从大到小）： * if(price < o.price){ return 1; } if(price > o.price){ return -1; } */
        @Override
        public int compare(ConsumInfo o1, ConsumInfo o2) {
             //首先比较price，如果price相同，则比较uid
            if(o1.getPrice() > o2.getPrice()){
                return 1;
            }
    
            if(o1.getPrice() < o2.getPrice()){
                return -1;
            }
    
            if(o1.getPrice() == o2.getPrice()){
                if(o1.getUid() > o2.getUid()){
                    return 1;
                }
                if(o1.getUid() < o2.getUid()){
                    return -1;
                }
            }
            return 0;
        }
    
    }
    
    
    /** * 需要进行比较的类 * @author breeze * */
    public class ConsumInfo{
        private int uid;
        private String name;
        private double price;
        private Date datetime;
    
        public ConsumInfo() {
            // TODO Auto-generated constructor stub
        }
    
        public ConsumInfo(int uid,String name,double price,Date datetime){
            this.uid = uid;
            this.name = name;
            this.price = price;
            this.datetime = datetime;
    
        }
    
        public int getUid() {
            return uid;
        }
    
        public void setUid(int uid) {
            this.uid = uid;
        }
    
        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 Date getDatetime() {
            return datetime;
        }
    
        public void setDatetime(Date datetime) {
            this.datetime = datetime;
        }
    
        @Override
        public String toString() {
            return "ConsumInfo [uid=" + uid + ", name=" + name + ", price=" + price
                    + ", datetime=" + datetime + "]";
        }
    
    }
    
    
    //测试类
    public class ConsumInfoTest {
    
        public static void main(String[] args) {
    
            ConsumInfo consumInfo1 = new ConsumInfo(100, "consumInfo1", 400.0,new Date());
            ConsumInfo consumInfo2 = new ConsumInfo(200, "consumInfo1", 200.0,new Date());
            ConsumInfo consumInfo3 = new ConsumInfo(300, "consumInfo1", 100.0,new Date());
            ConsumInfo consumInfo4 = new ConsumInfo(400, "consumInfo1", 700.0,new Date());
            ConsumInfo consumInfo5 = new ConsumInfo(500, "consumInfo1", 800.0,new Date());
            ConsumInfo consumInfo6 = new ConsumInfo(600, "consumInfo1", 300.0,new Date());
            ConsumInfo consumInfo7 = new ConsumInfo(700, "consumInfo1", 900.0,new Date());
            ConsumInfo consumInfo8 = new ConsumInfo(800, "consumInfo1", 400.0,new Date());
    
            List<ConsumInfo> list = new ArrayList<ConsumInfo>();
            list.add(consumInfo1);
            list.add(consumInfo2);
            list.add(consumInfo3);
            list.add(consumInfo4);
            list.add(consumInfo5);
            list.add(consumInfo6);
            list.add(consumInfo7);
            list.add(consumInfo8);
    
            System.out.println("排序前：");
            //排序前
            for(ConsumInfo consumInfo : list ){
                System.out.println(consumInfo);
            }
            ComparatorConsunInfo comparatorConsunInfo = new ComparatorConsunInfo();//比较器
            Collections.sort(list,comparatorConsunInfo);//排序
            System.out.println("排序后：");
            //排序后
            for(ConsumInfo consumInfo :list){
                System.out.println(consumInfo);
            }
        }
    }

--------------------

## 3. Comparator接口 ##

主要需要重写其中的compare(Object o1, Object o2)方法。

举例

package com.mxl.algorithlm;
    
    import java.util.Date;
    /** * 因为要实现对ConsumInfo对象的排序，所以在ConsunInfo类中要实现Comparable接口，也就是要实现compareTo()方法 * 具体的比较参照：依次按照price、uid进行倒序排序 * @author breeze * */
    public class ConsumInfo implements Comparable<ConsumInfo> {
        private int uid;
        private String name;
        private double price;
        private Date datetime;
    
        public ConsumInfo() {
            // TODO Auto-generated constructor stub
        }
    
        public ConsumInfo(int uid,String name,double price,Date datetime){
            this.uid = uid;
            this.name = name;
            this.price = price;
            this.datetime = datetime;
    
        }
    
        public int getUid() {
            return uid;
        }
    
        public void setUid(int uid) {
            this.uid = uid;
        }
    
        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 Date getDatetime() {
            return datetime;
        }
    
        public void setDatetime(Date datetime) {
            this.datetime = datetime;
        }
    
    
        @Override
        public String toString() {
            return "ConsumInfo [uid=" + uid + ", name=" + name + ", price=" + price
                    + ", datetime=" + datetime + "]";
        }
        /** * 这里比较的是什么, Collections.sort方法实现的就是按照此比较的东西排列 * 顺序（从小到大）： * if(price < o.price){ return -1; } if(price > o.price){ return 1; } * 倒序（从大到小）： * if(price < o.price){ return 1; } if(price > o.price){ return -1; } * */
        @Override
        public int compareTo(ConsumInfo o) {
            //首先比较price，如果price相同，则比较uid
            if(price < o.price){
                return -1;
            }
            if(price > o.price){
                return 1;
            }
    
            if(price == o.price){
                if(uid < o.uid){
                    return -1;
                }
                if(uid > o.uid){
                    return 1;
                }
            }
            return 0;
        }
    
    
    }
    
    //测试类
    
    package com.mxl.algorithlm;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Date;
    import java.util.List;
    
    public class ConsumInfoTest {
    
        public static void main(String[] args) {
    
            ConsumInfo consumInfo1 = new ConsumInfo(100, "consumInfo1", 400.0,new Date());
            ConsumInfo consumInfo2 = new ConsumInfo(200, "consumInfo1", 200.0,new Date());
            ConsumInfo consumInfo3 = new ConsumInfo(300, "consumInfo1", 100.0,new Date());
            ConsumInfo consumInfo4 = new ConsumInfo(400, "consumInfo1", 700.0,new Date());
            ConsumInfo consumInfo5 = new ConsumInfo(500, "consumInfo1", 800.0,new Date());
            ConsumInfo consumInfo6 = new ConsumInfo(600, "consumInfo1", 300.0,new Date());
            ConsumInfo consumInfo7 = new ConsumInfo(700, "consumInfo1", 900.0,new Date());
            ConsumInfo consumInfo8 = new ConsumInfo(800, "consumInfo1", 400.0,new Date());
    
            List<ConsumInfo> list = new ArrayList<ConsumInfo>();
            list.add(consumInfo1);
            list.add(consumInfo2);
            list.add(consumInfo3);
            list.add(consumInfo4);
            list.add(consumInfo5);
            list.add(consumInfo6);
            list.add(consumInfo7);
            list.add(consumInfo8);
            System.out.println("排序前：");
            //排序前
            for(ConsumInfo consumInfo : list ){
                System.out.println(consumInfo);
            }
    
            Collections.sort(list);//排序
            System.out.println("排序后：");
            //排序后
            for(ConsumInfo consumInfo :list){
                System.out.println(consumInfo);
            }
        }
    }

--------------------

## 4. 通用性排序器 ##

import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.Comparator; public class IdComparator<T> implements Comparator<T>{ private String attributeName; public IdComparator(){ } public IdComparator(String attributeName){ this.attributeName = attributeName; } public String getAttributeName() { return attributeName; } public void setAttributeName(String attributeName) { this.attributeName = attributeName; } /** * 如果o1小于o2,返回一个负数;如果o1大于o2，返回一个正数;如果他们相等，则返回0; */ @Override public int compare(T o1, T o2) { try { Class<? extends Object> tClass = o1.getClass(); Method method = tClass.getMethod(attributeName); Class<?> returnType = method.getReturnType(); Object obj = returnType.newInstance(); obj.getClass().getName(); if (returnType.newInstance() instanceof Integer) { // 可以替换为Number类 // 因为基本数据类型只有 Number类和 String类类型 Integer number1 = (Integer) method.invoke(o1); Integer number2 = (Integer) method.invoke(o2); if (number1 > number2) { return 1; } else if (number1 < number2) { return -1; } else { return 0; } }else if(returnType.newInstance() instanceof String){ String str1 = (String) method.invoke(o1); String str2 = (String) method.invoke(o2); if (str1.compareTo(str2) > 0) { return 1; } else if (str1.compareTo(str2) < 0) { return -1; } else { return 0; } } } catch (Exception ex) { ex.printStackTrace(); } return -1; } }

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## 5. 参考文献 ##

\[1\]. [Java中实现对象的比较：Comparable接口和Comparator接口][Java_Comparable_Comparator]  
\[2\]. [比较器：Compare接口与Comparator接口区别与理解][Compare_Comparator]

[Java_Comparable_Comparator]: http://www.cnblogs.com/Kevin-mao/p/5912775.html
[Compare_Comparator]: http://www.cnblogs.com/duange/p/6135943.html