在Java中实例化一个泛型类

问题描述

我知道Java的泛型与.Net相比有些逊色。我有一个泛型类 Foo< T> ，我真的需要使用无参数的构造函数在 Foo 中实例化 T 。如何解决Java的限制？

解决方案

一个选项是传入 Bar.class （或任何您感兴趣的类型 - 以任何方式指定适当的 Class< T> 引用）并将该值保留为字段：

  public class Test 
 {
 public static void main（String [] args）
 throws Exception //只是为了简单！ 
 {
通用< Bar> x =新的通用< Bar>（Bar.class）; 
 Bar y = x.buildOne（）; 
} 
} 
 
 public class Generic< T> 
 {
 private Class< T> clazz中; 
 
 public Generic（Class< T> clazz）
 {
 this.clazz = clazz; 
} 
 
 public T buildOne（）抛出InstantiationException，
 IllegalAccessException 
 {
 return clazz.newInstance（）; 
 
 
 
 public class Bar 
 {
 public Bar（）
 {
 System.out.println（构建）; 
} 
} 
  

另一种选择是有一个工厂并将工厂传递给泛型类的构造函数。这更加灵活，您不必担心反射异常。

I know Java's generics are somewhat inferior to .Net's.

I have a generic class Foo<T>, and I really need to instantiate a T in Foo using a parameter-less constructor. How can one work around Java's limitation?

解决方案

One option is to pass in Bar.class (or whatever type you're interested in - any way of specifying the appropriate Class<T> reference) and keep that value as a field:

public class Test
{
    public static void main(String [] args)
        throws Exception // Just for simplicity!
    {
        Generic<Bar> x = new Generic<Bar>(Bar.class);
        Bar y = x.buildOne();
    }
}

public class Generic<T>
{
    private Class<T> clazz;

    public Generic(Class<T> clazz)
    {
        this.clazz = clazz;
    }

    public T buildOne() throws InstantiationException,
        IllegalAccessException
    {
        return clazz.newInstance();
    }
}

public class Bar
{
    public Bar()
    {
        System.out.println("Constructing");
    }
}

Another option is to have a "factory" interface, and you pass a factory to the constructor of the generic class. That's more flexible, and you don't need to worry about the reflection exceptions.

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