利用ParameterizedType获取java泛型参数类

下面的代码将介绍如何利用ParameterizedType获取java泛型参数类型,进而通过反射获取java类。
<code class="hljs scala has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;">
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//超类</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">package</span> test;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.lang.reflect.ParameterizedType;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.lang.reflect.Type;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@SuppressWarnings</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"unchecked"</span>)
public <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 class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">T</span>> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Class<T> clazz;
    public Person() {
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 使用反射技术得到T的真实类型</span>
        ParameterizedType pt = (ParameterizedType) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.getClass().getGenericSuperclass(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获取当前new的对象的 泛型的父类 类型</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.clazz = (Class<T>) pt.getActualTypeArguments()[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获取第一个类型参数的真实类型</span>
        System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"clazz ---> "</span> + clazz);
    }

}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//子类</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">package</span> test;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.lang.reflect.ParameterizedType;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.lang.reflect.Type;

public <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-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Person</span><<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Student</span>> {</span>
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//测试类</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">package</span> test;

public <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);">TestGetClass</span> {</span>

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * <span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;">@param</span> args
     */</span>
    public static void main(String[] args) {

          Student student = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Student();
    }

}

</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: 1px solid 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></ul><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: 1px solid 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></ul>

显示效果 
这里写图片描述 
对反射的理解一步步深入,更多的实践和学习促进成长!

### Java对象的实例化 在 Java 中,要实例化带有的类或创建对象,通常有几种方式来实现这一点。 对于拥有无参数构造函数的类,可以直接通过 `new` 关键字来进行实例化[^1]: ```java MyGenericClass<String> myObject = new MyGenericClass<>(); ``` 当遇到不带无参构造器的情况时,则需借助反射机制中的 `Constructor<T>` 来完成实例化操作。下面是一个利用给定构造器并传入相应参数的例子[^4]: ```java public <T> T getNewObject(Constructor<T> cls, double d) { T t = null; try { t = cls.newInstance(d); } catch (Exception e) { e.printStackTrace(); } return t; } ``` 需要注意的是,在静态上下文中使用时,应该显式声明参数以确保编译期类安全[^2]。例如定义一个返回特定类的新实例的方法如下所示: ```java public static <T extends SomeBaseType> T createInstance(Class<T> clazz) throws Exception { return clazz.getDeclaredConstructor().newInstance(); } ``` 另外,由于Java 的类擦除特性,在运行时期间无法获取到实际的类信息,因此有时可能需要用到 `ParameterizedType` 接口配合反射技术处理更复杂的场景[^5]。 #### 使用自定义类作为例子展示对象的创建过程 考虑这样一个简单的类 `Person<E,T>` ,其中包含两个字段分别对应不同的 E 和 T 。这里展示了两种不同情况下此类的对象是如何被创建出来的: ```java class Person<E, T> { private final E name; // 构造函数接收单个参数用于初始化name属性 public Person(E name){ this.name = name; } @Override public String toString(){ return "Name:" + name ; } } // 创建时不提供具体类,默认为 Object 类 Person personWithoutTypeArgument = new Person<>("John"); // 明确指定了具体的类参数 Person<String,Integer> personWithTypeArguments = new Person<>("Alice"); ```
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