一、概述

Comparable和Comparator都是用来实现比较的，一般用于集合中元素的比较
基本包装类型，Integer、Long以及String都实现了Comparable接口，该接口的排序逻辑必须写在比较对象中，所以又叫自然排序
我们一般集合排序使用的Collections.sort()，默认使用的就是Comparable

 public static <T extends Comparable<? super T>> void sort(List<T> list) {list.sort(null);}

当然，我们也可以指定比较器，这里使用的就是Comparator了

 public static <T> void sort(List<T> list, Comparator<? super T> c) {list.sort(c);}

二、实际使用

1、Comparable

定义了对象Forlan，实现了Comparable接口，重写了compareTo(对象)方法

public class Forlan implements Comparable<Forlan> {private String name;/*** 身高*/private int height;/*** 体重*/private int weight;public Forlan(String name, int height, int weight) {this.name = name;this.height = height;this.weight = weight;}@Overridepublic String toString() {return "Forlan{" +"name='" + name + '\'' +", height=" + height +", weight=" + weight +'}';}/*** 比较身高*/@Overridepublic int compareTo(Forlan forlan) {return this.height - forlan.height;}
}

验证比较器

List<Forlan> list = new ArrayList<>();
Forlan forlan1 = new Forlan("身高低，体重中", 170, 130);
Forlan forlan2 = new Forlan("身高高，体重低", 180, 120);
Forlan forlan3 = new Forlan("身高中，体重高", 175, 140);
list.add(forlan1);
list.add(forlan2);
list.add(forlan3);
Collections.sort(list);
System.out.println(list);// 运行结果
[Forlan{name='身高低，体重中', height=170, weight=130}, Forlan{name='身高中，体重高', height=175, weight=140}, Forlan{name='身高高，体重低', height=180, weight=120}]

2、Comparator

定义了对象ForlanW，实现了Comparator接口，重写了compare(T o1, T o2)方法

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;public class ForlanW implements Comparator<ForlanW>{private String name;/*** 身高*/private int height;/*** 体重*/private int weight;public ForlanW(String name, int height, int weight) {this.name = name;this.height = height;this.weight = weight;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getWeight() {return weight;}public void setWeight(int weight) {this.weight = weight;}@Overridepublic String toString() {return "ForlanComparator{" +"name='" + name + '\'' +", height=" + height +", weight=" + weight +'}';}@Overridepublic int compare(ForlanW o1, ForlanW o2) {return o1.height - o2.height;}public static void main(String[] args) {List<ForlanW> list = new ArrayList<>();ForlanW forlan1 = new ForlanW("身高低，体重中", 170, 130);ForlanW forlan2 = new ForlanW("身高高，体重低", 180, 120);ForlanW forlan3 = new ForlanW("身高中，体重高", 175, 140);list.add(forlan1);list.add(forlan2);list.add(forlan3);// Collections.sort(list, new HeightComparator()); // 身高比较// Collections.sort(list, new WeightComparator()); // 体重比较// 身高比较Collections.sort(list, (ForlanW o1, ForlanW o2) -> {return o1.height - o2.height;});System.out.println(list);}
}class HeightComparator implements Comparator<ForlanW> {@Overridepublic int compare(ForlanW o1, ForlanW o2) {return o2.getHeight() - o1.getHeight();}
}class WeightComparator implements Comparator<ForlanW> {@Overridepublic int compare(ForlanW o1, ForlanW o2) {return o2.getWeight() - o1.getWeight();}
}

验证比较器

List<ForlanComparator> list = new ArrayList<>();
ForlanComparator forlan1 = new ForlanComparator("身高低，体重中", 170, 130);
ForlanComparator forlan2 = new ForlanComparator("身高高，体重低", 180, 120);
ForlanComparator forlan3 = new ForlanComparator("身高中，体重高", 175, 140);
list.add(forlan1);
list.add(forlan2);
list.add(forlan3);
// Collections.sort(list, new HeightComparator()); // 身高比较
// Collections.sort(list, new WeightComparator()); // 体重比较
// 身高比较
Collections.sort(list,(ForlanComparator o1, ForlanComparator o2)->{return o1.height - o2.height;
});
System.out.println(list);// 运行结果
[ForlanComparator{name='身高低，体重中', height=170, weight=130}, ForlanComparator{name='身高中，体重高', height=175, weight=140}, ForlanComparator{name='身高高，体重低', height=180, weight=120}]

三、总结

1、相同点

Comparable和Comparator都是用于比较排序

2、不同点

• 接口所在包不同：java.lang.Comparable、java.util.Comparator
• 比较逻辑不同：Comparable的在类中，Comparator可以在类中，也可以在类外，但在类中意义不大（简单来说，Comparable是内部比较器，Comparator是外部比较器）
• 排序方法不同：Comparable重写方法compareTo(T o)，Comparator重写方法compare(T o1, T o2)
• 在Collections.sort()中使用不同：一个参数，默认是Comparable自然排序，二个参数，需要传入Comparator外部排序
• 排序规则数量限制不同：Comparable唯一，Comparator可以有多个