Detailed description of the differences between Java Comparator Vs Comparable

1. Similarities between Comparator and Comparable

• Comparable & Comparator are both used to compare and sort elements in a collection;

• Comparable & Comparator are both java interfaces, Comparable is located under the package java.lang, and Comparator is located under the package java.util;

• If the custom class implements one of the two, you can compare the sizes.

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2. The difference between Comparator and Comparable

• Comparable is generally defined inside the class, while Comparator is generally defined outside the class ;

• To implement the Comparable interface, you need to rewrite its compareTo method, and to implement the Comparator interface, you need to rewrite its compare method Method;

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Implement Comparable interface method:

public class Person implements Comparable<Person> {

     private String name;     private int age;     @Override
     public int compareTo(Person another) {          int i = 0;
          i = name.compareTo(another.name);     // 使用String的compareTo方法
          if(i == 0) {      // 如果名字一样,比较年龄, 返回比较年龄结果
               return age - another.age;
          } else {               return i;    // 名字不一样, 返回比较名字的结果.
          }
     }
}

At this time, We can use Collections.sort( personList ) to sort.

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Implement the Comparator interface method:

public class Person{
     private String name;     private int age
}

public class PersonComparator implements Comparator<Person> { 
     public int compare(Person one, Person another) {          int i = 0;
          i = one.name.compareTo(another.name);     // 使用String的compareTo方法
          if(i == 0) {      // 如果名字一样,比较年龄,返回比较年龄结果
               return one.age - another.age;
          } else {               return i;    // 名字不一样, 返回比较名字的结果.
          }
     }
}

At this time, we can use Collections.sort(personList,new PersonComparator()) for sorting.

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3. Summary

• Using Comparable is relatively simple. As long as the object that implements the Comparable interface becomes An object that can be compared, but requires modifying the source code, and doing so will lead to relatively high code coupling, which will seriously affect the scalability of the code;

• The advantage of using Comparator is There is no need to modify the source code, and the code will not be strongly coupled , but implement another comparator. When a custom object needs to be compared, the size can be compared by passing the comparator and the object together;

So, from the perspective of code scalability, it would be better to implement the Comparator interface to sort the elements in the container.

Look at the following example:

public class HonorPerson extends Person{
     private String name;     private int age;     private STring degree;
}

　Here, the HonorPerson class cannot implement the Comparable interface again, because generics do not allow this, in other words In other words, the HonorPerson class can only use the comparison method of the Person class, and cannot define its own comparison method.

public class PersonComparator implements Comparator<Person>{}

public class HonorPersonComparator implements Comparator<HonorPerson>{}

　Here, HonorPerson and Person each have their own comparison methods, which do not affect or conflict with each other.

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