Guava学习（五）：ComparisonChain（比较链）

Guava学习（五）：ComparisonChain（比较链）

  主要作用是帮助我们实现对象的比较（如果对象有多个字段，我们希望比较的时候是根据多个字段来比较的），没用这个之前我们通常这样写：

 class Person implements Comparable {
     private String lastName;
     private String firstName;
     private int zipCode;
     public int compareTo(Person other) {
         int cmp = lastName.compareTo(other.lastName);
         if (cmp != 0) {
             return cmp;
         }
         cmp = firstName.compareTo(other.firstName);
         if (cmp != 0) {
             return cmp;
         }
         return Integer.compare(zipCode, other.zipCode);
     }
 }

  上面的代码太琐碎，不够优雅，使用ComparisonChain后就能帮助我们解决这个痛点了。话不多说，上代码。

Person类

package com.bluedragon.guavalearning.comparisonchain;

import com.google.common.collect.ComparisonChain;
import com.google.common.collect.Ordering;

/**
 * @author CodeRush
 * @date 2019/7/27 23:58
 */
public class Person implements Comparable<Person> {

    private String name;
    private Integer age;
    private Gender gender;

    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 Gender getGender() {
        return gender;
    }

    public void setGender(Gender gender) {
        this.gender = gender;
    }

    @Override
    public int compareTo(Person that) {
        //ComparisonChain执行一种懒比较： 它执行比较操作直至发现非零的结果， 在那之后的比较输入将被忽略,相对于下面的比较简单明了多了
        return ComparisonChain.start()
                .compare(this.name, that.name, Ordering.natural().nullsFirst())
                .compare(this.age, that.age)
                .compare(this.gender, that.gender)
                .result();
    }

//    class Person implements Comparable {
//        private String lastName;
//        private String firstName;
//        private int zipCode;
//        public int compareTo(Person other) {
//            int cmp = lastName.compareTo(other.lastName);
//            if (cmp != 0) {
//                return cmp;
//            }
//            cmp = firstName.compareTo(other.firstName);
//            if (cmp != 0) {
//                return cmp;
//            }
//            return Integer.compare(zipCode, other.zipCode);
//        }
//    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", gender=" + gender +
                '}';
    }

    /**
     * 性别枚举
     */
    public enum Gender {
        MAN,
        WOMAN
    }
}

测试类

package com.bluedragon.guavalearning.comparisonchain;

import com.google.common.collect.Lists;

import java.util.ArrayList;

/**
 * @author CodeRush
 * @date 2019/7/27 23:57
 */
public class ComparisonChainTest {

    public static void main(String[] args) {
        Person p1 = new Person();
        p1.setName("zs");
        p1.setAge(18);
        p1.setGender(Person.Gender.WOMAN);
        Person p2 = new Person();
        p2.setName("zs");
        p2.setAge(18);
        p2.setGender(Person.Gender.MAN);
        Person p3 = new Person();
        p3.setAge(18);
        p3.setGender(Person.Gender.MAN);
        Person p4 = new Person();
        p4.setName("zs");
        p4.setAge(20);
        p4.setGender(Person.Gender.MAN);

        ArrayList<Person> people = Lists.newArrayList(p1, p2, p3, p4);
        //使用ComparisonChain实现的compareTo方法排序集合
        people.sort(Person::compareTo);
        people.forEach(System.out::println);
    }
}