Java当中如何实现比较自定义类型的大小呢？
在Java当中，自定义类型不可以通过> < =来比较，一般有3种方式来实现：
Comparable、Comparator、equals()
今天先学习Comparable Comparator
1.Comparable接口
通过实现Comparable接口，重写CompareTo方法
class Student implements Comparable<Student>{
public String name;
public int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
@Override
public int compareTo(Student o) {
return this.age - o.age;
//根据年龄比较
//return this.name.compareTo(o.name);
}
}
public class TestComparable {
public static void main(String[] args) {
Student student1 = new Student("zhangsan",18);
Student student2 = new Student("lisi",28);
Student student3 = new Student("wangwu",38);
if (student1.compareTo(student2) > 0) {
System.out.println("student1的年龄大于student2的年龄");
}else if (student1.compareTo(student2) < 0) {
System.out.println("student1的年龄小于student2的年龄");
}else {
System.out.println("student1的年龄等于student2的年龄");
}
}
}
如果此时需要比较姓名的话，就需要重新实现CompareTo方法，同时这也是使用Comparable这种方法的弊端，一旦在类中写死，就只能修改类內部，不够灵活
2.Comparator接口
这个接口也被叫做比较器，先看具体的实现代码：
import java.util.Arrays;
import java.util.Comparator;
class Person {
public String name;
public int age;
public int score;
public Person(String name, int age, int score) {
this.name = name;
this.age = age;
this.score = score;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
", score=" + score +
'}';
}
}
class AgeComparator implements Comparator<Person> {
@Override
public int compare(Person o1, Person o2) {
//从小到大排序
return o1.age - o2.age;
}
}
class ScoreComparator implements Comparator<Person> {
@Override
public int compare(Person o1, Person o2) {
return o1.score - o2.score;
}
}
class NameComparator implements Comparator<Person> {
@Override
public int compare(Person o1, Person o2) {
return o1.name.compareTo(o2.name);
}
}
public class TestComparator {
//高级用法：使用Arrays.sort()方法传入比较器
public static void main(String[] args) {
Person person1 = new Person("aaa",18,80);
Person person2 = new Person("bbb",28,70);
Person person3 = new Person("ccc",38,60);
Person[] people = new Person[3];
people[0] = person1;
people[1] = person2;
people[2] = person3;
ScoreComparator scoreComparator = new ScoreComparator();
Arrays.sort(people,scoreComparator);
System.out.println(Arrays.toString(people));
}
public static void main1(String[] args) {
Person person1 = new Person("aaa",18,80);
Person person2 = new Person("bbb",28,70);
Person person3 = new Person("ccc",38,60);
//使用比较器进行比较
AgeComparator ageComparator = new AgeComparator();
System.out.println("根据年龄比较");
System.out.println(ageComparator.compare(person1,person2));
ScoreComparator scoreComparator = new ScoreComparator();
System.out.println("根据分数比较");
System.out.println(scoreComparator.compare(person2,person3));
NameComparator nameComparator = new NameComparator();
System.out.println("根据姓名比较");
System.out.println(nameComparator.compare(person3,person1));
}
}
直接定义一个类实现Comparator接口并重写compare()方法，想比较什么就直接定义，非常的灵活
同时Comparator还可以作为参数传递给Arrays.sort()方法，来规定他的比较方式
//高级用法：使用Arrays.sort()方法传入比较器
public static void main(String[] args) {
Person person1 = new Person("aaa",18,80);
Person person2 = new Person("bbb",28,70);
Person person3 = new Person("ccc",38,60);
Person[] people = new Person[3];
people[0] = person1;
people[1] = person2;
people[2] = person3;
ScoreComparator scoreComparator = new ScoreComparator();
Arrays.sort(people,scoreComparator);
System.out.println(Arrays.toString(people));
}
3.小结
Java在做自定义类型的比较的时候，通过实现这两个接口来完成，具体的细节看需求 Comparable
- 一般用于定义类的时候，实现该接口
- 注意重写方法：compareTo
- 优点：可以实现自定义类的比较方式
- 缺点：排序方式固定，不够灵活
Comparator
- 一般用于定义某个比较器的同时实现该接口
- 注意重写方法：compare
- 优点：可以根据不同的需求，进行不同的排序方式
- 缺点：必须自己建一个类进行排序
