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Java三大接口

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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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