java比较器

先来一个简单的实现

这里实现 Comparable 接口，重写compareTo方法实现排序，当两个对象进行比较时，返回0代表它们相等；返回值<0,代表this排在被比较对象之前；反之代表在被比较对象之后

package com.sun.comparator;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ComparatorDemo implements Comparable<ComparatorDemo> {

    private String name;
    private Integer age;
    private float score;

    public ComparatorDemo(String name, Integer age, float score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "name:" + name + ";age:" + age + ";score:" + score;
    }

    @Override
    public int compareTo(ComparatorDemo o) {
        if (this.score > o.score)// score是private的，为什么能够直接调用,这是因为在Student类内部
            return -1;// 由高到底排序
        else if (this.score < o.score)
            return 1;
        else {
            if (this.age > o.age)
                return 1;// 由底到高排序
            else if (this.age < o.age)
                return -1;
            else
                return 0;
        }
    }

    public static void main(String[] args) {
        List<ComparatorDemo> lists = new ArrayList<>();
        lists.add(new ComparatorDemo("a", 4, 4));
        lists.add(new ComparatorDemo("b", 3, 6));
        lists.add(new ComparatorDemo("c", 2, 3));
        lists.add(new ComparatorDemo("d", 1, 7));
        Collections.sort(lists);
        for (ComparatorDemo comparatorDemo : lists) {
            System.out.println("++++++" + comparatorDemo);
        }
        
        ComparatorDemo com[] = {new ComparatorDemo("a", 4, 4),
                new ComparatorDemo("b", 3, 6),
                new ComparatorDemo("c", 2, 3),
                new ComparatorDemo("d", 1, 7)};
        Arrays.sort(com);
        for (ComparatorDemo comparatorDemo : com) {
            System.out.println("------" + comparatorDemo);
        }
    }
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public float getScore() {
        return score;
    }

    public void setScore(float score) {
        this.score = score;
    }

}

 另一种方式

package com.sun.comparator;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class ComparatorDemo2 {

    private String name;
    private Integer age;
    private float score;

    public ComparatorDemo2(String name, Integer age, float score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "name:" + name + ";age:" + age + ";score:" + score;
    }


    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static void main(String[] args) {
        List<ComparatorDemo2> lists = new ArrayList<>();
        lists.add(new ComparatorDemo2("a", 4, 4));
        lists.add(new ComparatorDemo2("b", 3, 6));
        lists.add(new ComparatorDemo2("c", 2, 3));
        lists.add(new ComparatorDemo2("d", 1, 7));
        Comparator c = new ComparatorList();
        Collections.sort(lists, c);
        for (ComparatorDemo2 comparatorDemo : lists) {
            System.out.println("++++++" + comparatorDemo);
        }
        
        ComparatorDemo2 com[] = {new ComparatorDemo2("a", 4, 4),
                new ComparatorDemo2("b", 3, 6),
                new ComparatorDemo2("c", 2, 3),
                new ComparatorDemo2("d", 1, 7)};
        Arrays.sort(com, c);
        for (ComparatorDemo2 comparatorDemo : com) {
            System.out.println("------" + comparatorDemo);
        }
    }
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public float getScore() {
        return score;
    }

    public void setScore(float score) {
        this.score = score;
    }

}

package com.sun.comparator;

import java.util.Comparator;

public class ComparatorList  implements Comparator<ComparatorDemo2>{
    //我们也可以通过构造方法注入一些参数加入到比较中
    
    @Override
    public int compare(ComparatorDemo2 o1, ComparatorDemo2 o2) {
        if (o1.getScore() > o2.getScore())
            return -1;// 由高到底排序
        else if (o1.getScore() < o2.getScore())
            return 1;
        else {
            if (o1.getAge() > o2.getScore())
                return 1;// 由底到高排序
            else if (o1.getAge() < o2.getAge())
                return -1;
            else
                return 0;
        }
    }

}

 下面是多个属性联合排序，注意，这里使用BeanComparator实现

package com.sun.comparator;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import org.apache.commons.beanutils.BeanComparator;
import org.apache.commons.collections.ComparatorUtils;
import org.apache.commons.collections.comparators.ComparableComparator;
import org.apache.commons.collections.comparators.ComparatorChain;

public class ComplexComparator {
    private int  id;      
    private String  name;      
    private String age;      
    
    public ComplexComparator(){}
    
    public ComplexComparator(int id, String age,String name) {      
        this.id = id;      
        this.name = name;      
        this.age = age;      
    }  
    
    @SuppressWarnings({ "unchecked", "rawtypes" })  
    public static void main(String[] args) {      
      
        //在列表中加入若干ComplexComparator对象  
        ArrayList<Object> list = new ArrayList<Object>();      
        list.add(new ComplexComparator(1,"3","五"));      
        list.add(new ComplexComparator(1,"1","六"));      
        list.add(new ComplexComparator(1,"5","二"));      
        list.add(new ComplexComparator(1,"4","四"));      
        list.add(new ComplexComparator(4,"2","一"));      
  
        //创建一个排序规则  
        Comparator mycmp = ComparableComparator.getInstance();      
        mycmp = ComparatorUtils.nullLowComparator(mycmp);  //允许null         
        mycmp = ComparatorUtils.reversedComparator(mycmp); //逆序         
  
        //声明要排序的对象的属性，并指明所使用的排序规则，如果不指明，则用默认排序  
        ArrayList<Object> sortFields = new ArrayList<Object>();      
        sortFields.add(new BeanComparator("id", mycmp)); //id逆序  (主)      
        sortFields.add(new BeanComparator("age"));      //name正序 (副)   
  
        //创建一个排序链  
        ComparatorChain multiSort = new ComparatorChain(sortFields);   
  
        //开始真正的排序，按照先主，后副的规则  
        Collections.sort(list,multiSort);      
  
        for (int i =0;i<list.size();i++) {      
            System.out.println(list.get(i));    //输出      
        }      
        /** 
         * 输出结果如下: 
         * [id=4,name=2,age=一] 
         * [id=1,name=1,age=六] 
         * [id=1,name=3,age=五] 
         * [id=1,name=4,age=四] 
         * [id=1,name=5,age=二] 
         */  
    }      
      
    public int getId() {      
        return this.id;      
    }      
  
    public void setId(int id) {      
        this.id = id;      
    }      
  
    public String getName() {      
        return this.name;      
    }      
  
    public void setName(String name) {      
        this.name = name;      
    }      
  
    public String toString() {      
        return "[id=" + this.id + ",name=" + this.name +",age=" + this.age +"]";      
    }      
  
    public String getAge() {      
        return age;      
    }      
  
    public void setAge(String age) {      
        this.age = age;      
    }      
}

 按照某一项分组，然后按照另一项排序

package com.sun.comparator;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.apache.commons.beanutils.BeanComparator;
import org.apache.commons.collections.ComparatorUtils;

public class ComparatorUtilsDemo implements Comparator<ComparatorUtilsDemo> {
    private String name;
    private Integer age;
    private float score;
    public ComparatorUtilsDemo(){}
    
    public ComparatorUtilsDemo(String name, Integer age, float score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }
    
    @Override
    public int compare(ComparatorUtilsDemo o1, ComparatorUtilsDemo o2) {
        if (o1.getScore() > o2.getScore())
            return -1;// 由高到底排序
        else if (o1.getScore() < o2.getScore())
            return 1;
        else
            return 0;
    }
    
    @Override
    public String toString() {
        return "name:" + name + ";age:" + age + ";score:" + score;
    }
    
    public static void main(String[] args) {
        List<ComparatorUtilsDemo> lists = new ArrayList<>();
        lists.add(new ComparatorUtilsDemo("a", 4, 4));
        lists.add(new ComparatorUtilsDemo("d", 4, 4));
        lists.add(new ComparatorUtilsDemo("a", 4, 4));
        lists.add(new ComparatorUtilsDemo("c", 4, 4));
        lists.add(new ComparatorUtilsDemo("a", 4, 4));
        lists.add(new ComparatorUtilsDemo("b", 4, 4));
        lists.add(new ComparatorUtilsDemo("b", 3, 6));
        lists.add(new ComparatorUtilsDemo("c", 2, 3));
        lists.add(new ComparatorUtilsDemo("d", 1, 7));
        lists.add(new ComparatorUtilsDemo("a", 1, 7));
        Collections.sort(lists, ComparatorUtils.chainedComparator(new BeanComparator("name"), new ComparatorUtilsDemo()));
        for (ComparatorUtilsDemo c : lists) {
            System.out.println("++++++" + c);
        }
    }
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public float getScore() {
        return score;
    }

    public void setScore(float score) {
        this.score = score;
    }
}