java-面向对象之继承（感言：经过第一天和Java中类的继承和接口的实现的接触，自己需要学习的还很多，还要从基础抓起，尽管有点迷糊，但学到很多很喜欢这种时光！加油！）下面是查到的相关资料以备查看。

继承

一、概念

继承是面向对象三大特征之一。
当多个类中存在相同属性和行为时，可以将这些内容抽取到单独的一个类中，其他类只要继此类即可。这时，继承这个类的类称为子类，被继承的类称为父类或者超类。这样类与类之间就存在了继承的关系。
子类可以直接访问父类中的非私有的属性和行为。在代码中通过extends关键字表示继承关系。

二、特点

提高了代码的复用性。
让类与类之间产生了关系。有了这个关系，才有了多态的特性。

Tips

千万不要为了获取其他类中的功能，简化代码而继承。必须是类与类之间有所属关系才可以继承。

三、重点

在Java语言中，只支持单继承，不支持多继承，因为多继承容易带来安全隐患，就是当父类中定义了相同功能，当功能内容不同时，子类对象不确定要运行哪一个。但是Java保留了这种机制，并用另一种体现形式来完成表示，叫做多实现。
Java支持多层继承。
如何使用一个继承体系中的功能：先查阅父类体系的描述，因为父类中定义的是该体系的共性功能。通过了解共性功能，就可知该体系的基本功能。在具体调用时，要创建最子类的对象（父类不能创建对象；创建子类对象可以实现更多的功能）。

四、代码体现

子父类出现后，类成员的特点：

变量:如果子类中出现了非私有同名变量时，子类访问本类中的对象时用this，子类对象访问父类对象用super。（super的使用与this几乎一致，this本类对象引用，super父类对象的引用）

函数:当子类出现和父类一模一样的函数时，子类调用该函数，会执行子类函数的内容。这种情况是函数的另一个特性：重写（覆盖）。
覆盖注意事项： 

（1）.子类覆盖父类，必须保证子类的权限大于等于父类权限，才可以覆盖，否则编译失败。 

（2）.静态只能覆盖静态。 

（3）.与重载的区别：重载只看函数的参数列表；重写子类父类的方法一模一样。

构造函数 

在对子类对象进行初始化时，父类函数也会运行，因为子类的构造函数中第一行有一条隐示的语句super（）； super（）；会访问父类中空参数的构造函数。 
Q：为什么子类一定要访问父类的构造函数
A：因为父类中的数据子类可以直接获取，子类对象在建立时，需要先查看父类是如何对这些数据初始化的。

<code class="hljs axapta has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
* 例子：定义学生类和工人类，将学生和工人的共性提取出来，单独进行描述。
*   共性：name、age
*
* @author Qihuan
*
*/</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//定义一个person类</span>
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Person</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String name;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> age;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> speak(){
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"hello"</span>);
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String getName() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> name;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> setName(String name) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name = name;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> getAge() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> age;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> setAge(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> age) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.age = age;
}
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//学生类</span>
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Student</span> <span class="hljs-inheritance" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span></span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Person</span> {</span>
<span class="hljs-keyword" style="color:
4000
rgb(0, 0, 136); box-sizing: border-box;">void</span> study() {
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Student:"</span>+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Name: "</span>+getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Age:"</span>+getAge());
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> speak(){
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.speak();
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"study"</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重写</span>
}
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//工人类</span>
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Worker</span> <span class="hljs-inheritance" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span></span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Person</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> work() {
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Worker"</span>);
}
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ExtendsPractice</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> main(String[] args) {
Student stu = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Student();
stu.setAge(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>);
stu.setName(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"LiMing"</span>);
stu.study();
stu.speak();
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li></ul>

五、抽象类

概念

抽象就是从多个事物中将共性的，本质的内容抽取出来。

应用范围

当多个类中出现相同功能，但主体不同，这时可以只抽取功能定义，而不抽取主体。

特点

抽象方法一定定义在抽象类中。
抽象方法和抽象类都必须被abstract关键字修饰。
抽象类不可以用new创建对象，因为调用没有意义。
抽象类中的方法要被使用，必须由子类复写其所有的抽象方法后，建立子类对象调用。如果子类只覆盖了部分抽象方法，那么该子类还是一个抽象类。

Tips

抽象类中可以不定义抽象方法，这样做仅仅是不让该类建立对象。

代码体现

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/***************************************************
* 练习：假如我们在开发一个系统时需要对员工进行建模，员工包含3个属性：姓名、工号和工资。
* 经理也是员工，除了含有员工的属性之外，还有一个奖金属性。请使用继承的思想设计出员工类和经理类，类中提供必要的方法进行访问。
*<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @author</span> Qihuan
***************************************************
*/</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> class Employee {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String name;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String id;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> pay;

Employee(String name, String id, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> pay) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.setName(name);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.setId(id);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.setPay(pay);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">work</span>();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String <span class="hljs-title" style="box-sizing: border-box;">getName</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> name;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setName</span>(String name) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name = name;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String <span class="hljs-title" style="box-sizing: border-box;">getId</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> id;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setId</span>(String id) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.id = id;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> <span class="hljs-title" style="box-sizing: border-box;">getPay</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> pay;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setPay</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> pay) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.pay = pay;
}
}

class Pro extends Employee {

Pro(String name, String id, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> pay) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(name, id, pay);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">work</span>() {
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"professional work"</span>);
}

}

class Manager extends Employee {

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span
11865
class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> bonus;

Manager(String name, String id, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> pay, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> bonus) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(name, id, pay);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.setBonus(bonus);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">work</span>() {
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"manager work"</span>);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getBonus</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> bonus;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setBonus</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> bonus) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.bonus = bonus;
}

}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AbstractPractice</span> {</span>

}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li></ul>

抽象类的注意事项

被abstract修饰的函数不能同时被private、final、static修饰。 
final：被final修饰的类不能有子类。而被abstract修饰的类一定是一个父类。
private:抽象类中的私有的抽象方法，不被子类所知，就无法被复写，而抽象方法出现的就是需要被复写。
static：如果static可以修饰抽象方法，那么连对象都省了，直接类名调用就可以了。可是抽象方法运行没意义。

抽象类中可以不定义抽象方法。这样做可以不让本来实例化，也可以用于模块设计。

模板方法设计模式（Template）

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
* 模板方法设计模式（Template）：
*      在定义功能时，功能的一部分，是确定的，但是有一部分是不确定的，而确定的
*      的部分在使用不确定的部分，那么就将不确定的部分暴露出去，由该子类完成。
*
* 需求：获取一段程序的运行时间
* 原理：获取程序开始和结束的时间，并相减。
* Tips：获取时间 - System.currentTimeMillis();
*<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @author</span> Qihuan
*
*/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">GetTime</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">getTime</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> start = System.currentTimeMillis();

runCode();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> end = System.currentTimeMillis();

System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Time = "</span>+(end - start));
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">runCode</span>();
}

class SubTime extends GetTime {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">runCode</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4000</span>; i++) {
System.out.println(i);
}
}
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">TemplatePractice</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {
SubTime gt = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SubTime();
gt.getTime();
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li></ul>

六、接口

概念

可以认为是一个特殊的抽象类，当类中的方法都是抽象的，那么该类可以通过接口的形式来表示。

格式

接口中常见定义：常量、抽象方法。
接口中的成员都有固定的修饰符 

（1）常量：public static final 

（2）方法：public abstract

注意事项

接口中的成员都是public的。
接口是不可以创建对象的，因为有抽象方法，需被子类实现，子类接口中的抽象方法全被覆盖后，子类才可以被实例化，否则子类就是一个抽象类。
接口可以被类多实现，也是对多继承不支持的转换形式。Java支持多实现。

特点

接口是对外暴露的规则。
接口是程序的功能扩展。
接口可以用来多实现。
类与接口之间是实现关系，而且类可以继承一个类的同时实现多个接口。
接口与接口之间可以有继承关系。

代码体现

<code class="hljs axapta has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterDemo</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> NUM = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> show();
}

<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterDemo1</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> NEW_NUM = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">abstract</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> show1();
}

<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterTest</span> <span class="hljs-inheritance" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span></span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterDemo</span>,<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterDemo1</span> {</span>

@Override
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> show() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub</span>
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Test Interface :: "</span>+NUM);
}

@Override
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> show1() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub</span>
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Test Interface （多实现）:: "</span>+NEW_NUM);
}

}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">InterfacePractice</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> main(String[] args) {
InterTest it = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> InterTest();
it.show();
it.show1();
}
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li></li></ul>