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【java对象比较器和克隆】

时间：2024-3-2 17:57     作者：韩俊     分类： Android

一.比较器Comparable和Comparator

       上一篇博客介绍了工具类Arrays工具类。我们可以对基本类型的数组调用Arrays.sort()函数来进行数组的排序。排序操作在日常开发中经常要使用到。那么String类和自定义类能不能使用Arrays.sort()来进行排序呢。下面我们来试试，如下：

public class Mystring { 

  <br style="word-wrap:break-word">

public static void main(String[] args) {  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

   String []a={&quot;早上&quot;,&quot;中午&quot;,&quot;下午&quot;,&quot;傍晚&quot;,&quot;晚上&quot;};  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Person[] b={ new Person(&quot;小白&quot;,15),new Person(&quot;小黑&quot;,19),  <br style="word-wrap:break-word">

                new Person(&quot;小红&quot;,14),new Person(&quot;小紫&quot;,20)};     <br style="word-wrap:break-word">

   Arrays.sort(a);  <br style="word-wrap:break-word">

   for(int i=0;i&lt;a.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.print(a[i]);  <br style="word-wrap:break-word">

   System.out.print(&quot;rn&quot;);  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Arrays.sort(b);  <br style="word-wrap:break-word">

   for(int i=0;i&lt;b.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.println(b[i]);  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

}

//自定义类

class Person { 

  <br style="word-wrap:break-word">

public String name;  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

public int age;   <br style="word-wrap:break-word">


public Person(String name,int age) {  <br style="word-wrap:break-word">

    this.name=name;  <br style="word-wrap:break-word">

    this.age=age;  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">


}

复制代码
程序运行结果：


我们发现String可以调用Arrays.sort()函数，而我们自定义的Person类报错，看错误的关键字 Comparable

打开String源码


由此引入比较器Comparable，我们下面利用Comparable接口来实现Person使用Arrays.sort()按年龄排序递增排序。

Comparable接口能够对实现它的类的对象进行排序，主要使用compareTo函数来实现排序。compareTo函数返回int类型，分别返回-1,0,1对应小于，等于，大于。


把代码改为：

public class Mystring { 

  <br style="word-wrap:break-word">

public static void main(String[] args) {  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

   String []a={&quot;早上&quot;,&quot;中午&quot;,&quot;下午&quot;,&quot;傍晚&quot;,&quot;晚上&quot;};  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Person[] b={ new Person(&quot;小白&quot;,15),new Person(&quot;小黑&quot;,19),  <br style="word-wrap:break-word">

                new Person(&quot;小红&quot;,14),new Person(&quot;小紫&quot;,20)};     <br style="word-wrap:break-word">

   Arrays.sort(a);  <br style="word-wrap:break-word">

   for(int i=0;i&lt;a.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.print(a[i]);  <br style="word-wrap:break-word">

   System.out.print(&quot;rn&quot;);  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Arrays.sort(b);  <br style="word-wrap:break-word">

   for(int i=0;i&lt;b.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.println(b[i]);  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

}

//自定义类

class Person implements Comparable<Person>{ 

  <br style="word-wrap:break-word">

public String name;  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

public int age;   <br style="word-wrap:break-word">


public Person(String name,int age) {  <br style="word-wrap:break-word">

    this.name=name;  <br style="word-wrap:break-word">

    this.age=age;  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

//比较器的比较函数  <br style="word-wrap:break-word">

/** <br style="word-wrap:break-word">

 * 如果当前对象小于比较对象，返回-1 <br style="word-wrap:break-word">

 * 如果当前对象等于比较对象，返回0 <br style="word-wrap:break-word">

 * 如果当前对象大于比较对象，返回1 <br style="word-wrap:break-word">

 */  <br style="word-wrap:break-word">

@Override  <br style="word-wrap:break-word">

public int compareTo(Person o) {  <br style="word-wrap:break-word">

    //对象为空，抛出空指针异常  <br style="word-wrap:break-word">

    if(o==null)  <br style="word-wrap:break-word">

        throw new NullPointerException();  <br style="word-wrap:break-word">

    if(this.age&lt;o.age)  <br style="word-wrap:break-word">

        return -1;  <br style="word-wrap:break-word">

    if(this.age&gt;o.age)  <br style="word-wrap:break-word">

        return 1;  <br style="word-wrap:break-word">

    return 0;  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

//重写toString方法  <br style="word-wrap:break-word">

@Override  <br style="word-wrap:break-word">

public String toString() {  <br style="word-wrap:break-word">

    return &quot;Person [name=&quot; &#43; name &#43; &quot;, age=&quot; &#43; age &#43; &quot;]&quot;;  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">


}

复制代码





为自定义的Person实现比较器Comparable接口，即可调用Arrays.sort（）进行排序。


另外还有另一种实现方法，实现Comparator接口。

public class Mystring { 

  <br style="word-wrap:break-word">

public static void main(String[] args) {  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

   String []a={&quot;早上&quot;,&quot;中午&quot;,&quot;下午&quot;,&quot;傍晚&quot;,&quot;晚上&quot;};  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Person[] b={ new Person(&quot;小白&quot;,15),new Person(&quot;小黑&quot;,19),  <br style="word-wrap:break-word">

                new Person(&quot;小红&quot;,14),new Person(&quot;小紫&quot;,20)};     <br style="word-wrap:break-word">

   Arrays.sort(a);  <br style="word-wrap:break-word">

   for(int i=0;i&lt;a.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.print(a[i]);  <br style="word-wrap:break-word">

   System.out.print(&quot;rn&quot;);  <br style="word-wrap:break-word">

     <br style="word-wrap:break-word">

   Arrays.sort(b,new PersonComparator());  <br style="word-wrap:break-word">

   for(int i=0;i&lt;b.length;i&#43;&#43;)  <br style="word-wrap:break-word">

       System.out.println(b[i]);  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

}

//自定义类

class Person { 

public String name;  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

public int age;   <br style="word-wrap:break-word">


public Person(String name,int age) {  <br style="word-wrap:break-word">

    this.name=name;  <br style="word-wrap:break-word">

    this.age=age;  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

@Override  <br style="word-wrap:break-word">

public String toString() {  <br style="word-wrap:break-word">

    return &quot;Person [name=&quot; &#43; name &#43; &quot;, age=&quot; &#43; age &#43; &quot;]&quot;;  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">


}


class PersonComparator implements Comparator<Person>{ 


 //比较器的比较函数  <br style="word-wrap:break-word">

    /** <br style="word-wrap:break-word">

     * 如果当前对象小于比较对象，返回-1 <br style="word-wrap:break-word">

     * 如果当前对象等于比较对象，返回0 <br style="word-wrap:break-word">

     * 如果当前对象大于比较对象，返回1 <br style="word-wrap:break-word">

     */  <br style="word-wrap:break-word">

@Override  <br style="word-wrap:break-word">

public int compare(Person o1, Person o2) {  <br style="word-wrap:break-word">

    //对象为空，抛出空指针异常  <br style="word-wrap:break-word">

    if(o1==null||o2==null)  <br style="word-wrap:break-word">

        throw new NullPointerException();  <br style="word-wrap:break-word">

    if(o1.age&lt;o2.age)  <br style="word-wrap:break-word">

        return -1;  <br style="word-wrap:break-word">

    if(o1.age&gt;o2.age)  <br style="word-wrap:break-word">

        return 1;  <br style="word-wrap:break-word">

    return 0;  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

}

复制代码

二.对象的克隆Clone

将一个对象复制一份，称作对象的克隆技术。克隆对象分为两步。

1.实现Cloneable标记接口

   Cloneable是一个标记接口，此接口没有定义任何方法。只是作为一个标记给虚拟机。

2.重写Object的clone方法

//自定义类person实现Cloneable接口

class Person implements Cloneable { 

public String name;  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

public int age;   <br style="word-wrap:break-word">


public Person(String name,int age) {  <br style="word-wrap:break-word">

    this.name=name;  <br style="word-wrap:break-word">

    this.age=age;  <br style="word-wrap:break-word">

      <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">

//重写Object的clone方法  <br style="word-wrap:break-word">

@Override  <br style="word-wrap:break-word">

protected Object clone() throws CloneNotSupportedException  <br style="word-wrap:break-word">

{  <br style="word-wrap:break-word">

    return super.clone();  <br style="word-wrap:break-word">

}  <br style="word-wrap:break-word">


}

复制代码
克隆的调用：

public static void main(String[] args) { 

      <br style="word-wrap:break-word">

     Person temp=new Person(&quot;王&#23612;玛&quot;,18);  <br style="word-wrap:break-word">

       <br style="word-wrap:break-word">

     try {  <br style="word-wrap:break-word">

        Person ok=(Person)temp.clone();//把Object类转化为Person、  <br style="word-wrap:break-word">

        System.out.println(ok.name);//输出王&#23612;玛  <br style="word-wrap:break-word">

    } catch (CloneNotSupportedException e) {  <br style="word-wrap:break-word">

        e.printStackTrace();  <br style="word-wrap:break-word">

    }  <br style="word-wrap:break-word">

  <br style="word-wrap:break-word">

}

复制代码
这样既可以完成对一个对象的克隆，当我们要创建一系列类似的对象时，可以考虑使用克隆技术可以得到更好的性能，比你new创建好一些

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