Comparable和Comparator接口

最新推荐文章于 2025-08-06 16:23:50 发布

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最新推荐文章于 2025-08-06 16:23:50 发布

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文章标签： java

原文链接：https://my.oschina.net/wuyiyi/blog/860364

本文详细介绍了Java中通过Comparable和Comparator接口实现对象排序的方法，并提供了具体的示例代码，展示了如何实现升序和降序排列。

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java中通过接口实现两个对象的比较，常用的就是Comparable和Comparator接口。

Comparable：位于java.lang包

Comparator：位于java.util包

排序通常使用的方法是：

Collections.sort(List<T> list)

或者

Collections.sort(List<T> list, Comparator<? super T> c)

根据排序的方法可以看到，一种是对象本身实现了排序，一种是实现Comparator接口的排序。具体使用如下所示：

一、Comparable：

Comparable接口将比较代码嵌入需要进行比较的类的自身代码中。此接口强行对实现它的每个类的对象进行整体排序。此排序被称为该类的自然排序，类的CompareTo方法被称为它的自然比较方法。实现此接口的对象列表可以通过Collections.sort(和Arrays.sort)进行自动排序。实现此接口的对象可以用作有序映射表中的键或有序集合中的元素，无需指定比较器。

示例：

/**
 * 因为要实现对ConsumInfo对象的排序，所以ConsumInfo类中要实现Comparable接口
 * 也就是要实现compareTo()方法
 */
public class ConsumInfo implements Comparable<ConsumInfo> {
    private int uid;
    private String name;
    private double price;
    private Date datetime;

    public ConsumInfo() {
    }

    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 +
                '}';
    }

    public int compareTo(ConsumInfo o) {
       //升序排序
        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：
public class ConsumIofoTest {
    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");
        for (ConsumInfo consumInfo : list){
            System.out.println(consumInfo);
        }
        Collections.sort(list);
        System.out.println("排序后");
        for (ConsumInfo consumInfo :list){
            System.out.println(consumInfo);
        }
    }
}

二、Comparator：

Comparator接口在一个独立的类中实现。如果前期类的设计没有考虑到类的Compare问题而没有实现Comparable接口，后期可以通过Comparator接口实现比较算法进行排序。

示例：

//要进行比较的类
public class ConsumInfo{
    private int uid;
    private String name;
    private double price;
    private Date datetime;

    public ConsumInfo() {
    }

    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 +
                '}';
    }
}

//实现Comparator接口的比较器
public class ComparatorConsunInfo implements Comparator<ConsumInfo> {
    public int compare(ConsumInfo o1, ConsumInfo o2) {
        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;
    }
}

//测试类
public class ConsumIofoTest {
    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");
        for (ConsumInfo consumInfo : list){
            System.out.println(consumInfo);
        }
        ComparatorConsunInfo comparatorConsunInfo = new ComparatorConsunInfo();
        Collections.sort(list,comparatorConsunInfo);
        System.out.println("排序后");
        for (ConsumInfo consumInfo :list){
            System.out.println(consumInfo);
        }
    }
}

今天想对一个集合进行排序，看了自己写的文章，竟然没看懂。因为说到排序，自然有升序和降序。但是上述篇幅都没有说到。。。。。

现在补充一下：

对于Comparable方式来说：

public int compareTo(BeanClass bc) {
		//return this.para - bc.para; //升序
		return bc.para-this.para; //降序
	}

对于Comparator：方式来说

  @Override
    public int compare(BeanClass o1, BeanClass o2) {
        //return o1.para-o2.para;  //升序
        return o2.para-o1.para;  //降序
    }

转载于:https://my.oschina.net/wuyiyi/blog/860364