Comparable接口和Comparator接口它们的区别与使用方式

Comparable接口

此接口只包含一个compareTo(T t)方法。
这个方法可以个给两个对象排序。返回值类型为int，它返回负数，0，正数来表明已经存在的对象小于，等于，大于输入对象。

此方法一般写在传入的集合元素中，让元素继承此接口，重写上述方法。例子如下：

package com.qianfeng.weekendDay03;

public class Student implements Comparable<Object>{
	
	private String number;
	private String name;
	private int age;
	private String e_mail;
	private String phone;
	
	public Student() {
		super();
	}
	
	public Student(String number, String name, int age, String e_mail, String phone) {
		super();
		this.number = number;
		this.name = name;
		this.age = age;
		this.e_mail = e_mail;
		this.phone = phone;
	}
	
	@Override
	public String toString() {
		return "Student [学号为：" + number + ", 姓名为：" + name + ", 年龄为：" + age + ", e_mail为：" + e_mail + ", 手机号为："
				+ phone + "]";
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((e_mail == null) ? 0 : e_mail.hashCode());
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		result = prime * result + ((number == null) ? 0 : number.hashCode());
		result = prime * result + ((phone == null) ? 0 : phone.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (age != other.age)
			return false;
		if (e_mail == null) {
			if (other.e_mail != null)
				return false;
		} else if (!e_mail.equals(other.e_mail))
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		if (number == null) {
			if (other.number != null)
				return false;
		} else if (!number.equals(other.number))
			return false;
		if (phone == null) {
			if (other.phone != null)
				return false;
		} else if (!phone.equals(other.phone))
			return false;
		return true;
	}

	public String getNumber() {
		return number;
	}

	public void setNumber(String number) {
		this.number = number;
	}

	public String getName() {
		return name;
	}

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

	public int getAge() {
		return age;
	}

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

	public String getE_mail() {
		return e_mail;
	}

	public void setE_mail(String e_mail) {
		this.e_mail = e_mail;
	}

	public String getPhone() {
		return phone;
	}

	public void setPhone(String phone) {
		this.phone = phone;
	}

	//重写比较器方法
	@Override
	public int compareTo(Object o) {
		return this.age - ((Student)o).getAge();
	}
	
}

package com.qianfeng.day14;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

import com.qianfeng.weekendDay03.Student;

public class TreeSetTest {
	public static void main(String[] args) {
		Set<Student> set=new TreeSet<>();
		
		Student[] student = new Student[5];
		student[0] = new Student("1001","张三",18,"12345@qq.com","15675636271");
		student[1] = new Student("1002","李四",19,"54321@qq.com","18366543271");
		student[2] = new Student("1003","王五",28,"98765@qq.com","12365736271");
		student[3] = new Student("1004","赵六",20,"13534@qq.com","19887532271");
		student[4] = new Student("1005","田七",22,"56789@qq.com","16765736271");
		
		for(int i = 0; i < 5; i++) {
			set.add(student[i]);
		}
		System.out.println(set);
		//结果按年龄从小到大排列输出
	}
}

Comparator接口

此接口一般使用int compare(T o1, T o2);方法。
这个方法可以个给两个对象排序。返回值类型为int，它返回负数，0，正数来表明已经存在的对象小于，等于，大于输入对象。

此方法一般写在接口的实现类中，一般用于集合中的sort方法传入。或者用于TreeSet或TreeMap集合的构造器中。例子如下：

package com.qianfeng.day14;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

import com.qianfeng.weekendDay03.Student;

public class TreeSetTest {
	public static void main(String[] args) {
		//采用匿名内部类的方式或者用lambda表达式也行
		Set<Student> set=new TreeSet<>(new Comparator<Student>() {
	        public int compare(Student o1, Student o2) {
	            return o1.getAge()-o2.getAge();
	        }
	    });
	    //Set<Student> set=new TreeSet<>((s1,s2)->s1.getAge()-s2.getAge());

		Student[] student = new Student[5];
		student[0] = new Student("1001","张三",18,"12345@qq.com","15675636271");
		student[1] = new Student("1002","李四",19,"54321@qq.com","18366543271");
		student[2] = new Student("1003","王五",28,"98765@qq.com","12365736271");
		student[3] = new Student("1004","赵六",20,"13534@qq.com","19887532271");
		student[4] = new Student("1005","田七",22,"56789@qq.com","16765736271");
		
		for(int i = 0; i < 5; i++) {
			set.add(student[i]);
		}
		System.out.println(set);
	}
}

两接口之间的相同点

都是用于集合元素间的比较，排序操作