Java的Comparable,Comparator和Cloneable三大接口详解
作者:反内码者
1、比较器
①比较器的引入
a.首先,当我们单一地比较某一种数据类型的数组时,可以直接用Arrays.sort()进行实现
b.而当我们同时含有多个参数时,并没有告诉我们按照什么来进行排序,此时,若是用Arrays.sort()就会出现报错的情况
基于这种情况,我们了解到,若是要将自定义类型进行大小比较 ,就要引入能够实现比较的接口,下面我们介绍Comparable和Comparator这两种比较器
1.1Comparable接口
①实现Comparable接口的操作
②通过Comparable接口实现年龄的排序
③通过Comparable来实现名字的排序(注意名字是引用类,比较时应该是用compareTo()来进行)
④升序降序
由于最终是利用的Arrays.sort()进行的比较,该方法底层是升序的操作,若是想转换为降序,只需要将重写的compareTo()方法中两项互换位置即可
变为降序后代码运行结果:
⑤缺点!!!
Comparable对类的倾入性很强。由上面我们可知,要想比较新的类型就要更改compareTo()中的类型重新进行比较,这个在以后的工作中极大可能会使整个代码出现逻辑问题,可读性问题,因此我们引入下一类很灵活,倾入性不强的Comparator接口
⑥整体代码如下:
import java.util.Arrays; class Student implements Comparable<Student> { public int age; public String name; public double score; public Student(int age,String name,double score){ this.age=age; this.name=name; this.score=score; } @Override public String toString() { return "Student{" + "age=" + age + ", name='" + name + '\'' + ", score=" + score + '}'; } public static void main3(String[] args) { Student student1=new Student(12,"张三",98.0); Student student2=new Student(18,"李四",97.9); //if(student1.compareTo(student2)>0)返回1;根据下面的方法进行进一步的返回 System.out.println(student1.compareTo(student2)); } public static void main(String[] args) { Student []student=new Student[3]; student[0]=new Student(36,"zhangsan",98.0); student[1]=new Student(18,"lisi",97.9); student[2]=new Student(27,"wangwu",65.3); System.out.println(Arrays.toString(student)); Arrays.sort(student); System.out.println(Arrays.toString(student)); } public static void main1(String[] args) { int []array=new int []{2,5,3,6,8}; System.out.println(Arrays.toString(array)); Arrays.sort(array); System.out.println(Arrays.toString(array)); } @Override //谁调用这个方法,谁就是this public int compareTo(Student o) { //return this.age-o.age; return o.name.compareTo(this.name); } }
1.2Comparator接口
①实现Comparable接口的操作:
②通过该接口实现的姓名的比较:
③升序降序
执行后的结果:
④优点
灵活,对类的倾入性不强
⑤整体代码如下:
import java.util.Arrays; import java.util.Comparator; class Student { public int age; public String name; public double score; public Student(int age, String name, double score) { this.age = age; this.name = name; this.score = score; } @Override public String toString() { return "Student{" + "age=" + age + ", name='" + name + '\'' + ", score=" + score + '}'; } } class AgeComparator implements Comparator<Student> { @Override public int compare(Student o1, Student o2) { return o1.age-o2.age; } } class ScoreComparator implements Comparator<Student> { @Override public int compare(Student o1, Student o2) { return (int)(o1.score-o2.score); } } class NameComparator implements Comparator<Student> { @Override public int compare(Student o1, Student o2) { return o1.name.compareTo(o2.name); } } public class Test { public static void main2(String[] args) { Student students1 = new Student(1,"bit",98.9); Student students2 = new Student(2,"abc",88.9); /* if(students1.compareTo( students2) > 0) { }*/ //System.out.println(students1.compareTo( students2)); AgeComparator ageComparator = new AgeComparator(); System.out.println(ageComparator.compare(students1,students2)); } public static void main(String[] args) { Student[] student = new Student[3]; student[0] = new Student(12,"lisi",98.9); student[1] = new Student(6,"zangwu",88.9); student[2] = new Student(18,"whangsan",18.9); System.out.println(Arrays.toString(student)); AgeComparator ageComparator = new AgeComparator(); ScoreComparator scoreComparator = new ScoreComparator(); NameComparator nameComparator = new NameComparator(); Arrays.sort(student,nameComparator);//默认是从小到大的排序 System.out.println(Arrays.toString(student)); } public static void main1(String[] args) { int[] array = {1,21,3,14,5,16}; System.out.println(Arrays.toString(array)); Arrays.sort(array); System.out.println(Arrays.toString(array)); } }
2、Cloneable接口
①如何实现Cloneable接口:
Object 类中存在一个 clone 方法, 调用这个方法可以创建一个对象的 "拷贝". 但是要想合法调用 clone 方法, 必须要先实现 Clonable 接口, 否则就会抛出 CloneNotSupportedException
异常。
a.实现Cloneable接口
b.重写Cloneable方法
c.抛异常,强制类型转换
②面试中常问问题:
你知道Cloneable接口吗?为什么它是一个空接口,它有什么作用呢?
空接口,标志接口,代表这个类是可以被克隆的
③克隆的原理图:
④整体代码的实现:
class Person implements Cloneable{ public int age; public void eat(){ System.out.println("吃!"); } @Override public String toString() { return "Person{" + "age=" + age + '}'; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } public class TestDemo { public static void main(String[] args) throws CloneNotSupportedException { Person person = new Person(); person.age=13; Person person2=(Person)person.clone(); System.out.println(person2); System.out.println(person); System.out.println("==========="); person2.age=14; System.out.println(person); System.out.println(person2); } }
2.1深拷贝和浅拷贝
①深浅拷贝:
决定是深拷贝还是浅拷贝,并不是方法的用途,而是代码的实现
②浅拷贝示例
浅拷贝代码如下:
class Money implements Cloneable{ public double m = 12.5; } class Person implements Cloneable{ public int age; public Money money = new Money(); public void eat() { System.out.println("吃!"); } @Override public String toString() { return "Person{" + "age=" + age + '}'; } @Override protected Object clone() throws CloneNotSupportedException { Person tmp = (Person)super.clone(); return tmp; } } public class TestDemo { public static void main(String[] args) throws CloneNotSupportedException { Person person = new Person(); Person person2 = (Person)person.clone(); System.out.println(person.money.m); System.out.println(person2.money.m); System.out.println("====================="); person2.money.m = 98.5; System.out.println(person.money.m); System.out.println(person2.money.m); } }
③深拷贝示例:(将tmp中的money也进行拷贝)
深拷贝代码如下:
class Money implements Cloneable{ public double m = 12.5; @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } class Person implements Cloneable{ public int age; public Money money = new Money(); public void eat() { System.out.println("吃!"); } @Override public String toString() { return "Person{" + "age=" + age + '}'; } @Override protected Object clone() throws CloneNotSupportedException { Person tmp = (Person)super.clone(); tmp.money = (Money) this.money.clone(); return tmp; //return super.clone(); } } public class TestDemo { public static void main(String[] args) throws CloneNotSupportedException { Person person = new Person(); Person person2 = (Person)person.clone(); System.out.println(person.money.m); System.out.println(person2.money.m); System.out.println("====================="); person2.money.m = 98.5; System.out.println(person.money.m); System.out.println(person2.money.m); } }
总结
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