在Java中创建的T新实例 [英] Create new instance of T in Java
问题描述
在C#中,我们可以定义一个通用类A< T>其中T:new()
。在这段代码中,我们可以用 new T()
创建一个 T
的实例。这在Java中如何实现?我读了一些文章说这是不可能的。
in C#, we can define a generic class A<T> where T : new()
. In this code, we can create an instance of T
with new T()
. How does this implement in Java? I read some article which says it's impossible.
我使用的原因是在C#中使用泛型使用单例模式:
The reason that I used have a singleton patten using generic in C# like:
public static class Singleton<T> where T : new()
{
private static T instance;
public static T Instance
{
get
{
if (instance == null)
{
instance = SingletonCreater.Instance;
}
return instance;
}
}
static class SingletonCreater
{
internal static readonly T Instance = new T();
}
}
还有更好的方法吗? p>
And way to make this method more graceful?
推荐答案
没有你不能做新的T(),因为你不知道T是否有一个没有arg构造函数,由于类型删除,T的类型在运行时不存在。
No you can't do new T(), since you don't know if T has a no arg constructor, and because the type of T is not present at runtime due to type erasure.
要创建T的实例,您需要具有
To create an instance of T, you need to have code like,
public <T> T create(Class<T> clazz) {
try {
//T must have a no arg constructor for this to work
return clazz.newInstance();
} catch (InstantiationException e) {
throw new IllegalStateException(e);
} catch (IllegalAccessException e) {
throw new IllegalStateException(e);
}
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