Illegal class literal for the type parameter T错误解决方法

最新推荐文章于 2022-10-21 10:59:35 发布

原创最新推荐文章于 2022-10-21 10:59:35 发布 · 1.1k 阅读

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#java #开发工具 #runtime

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本文解决了一个关于Java泛型编程中出现的“非法泛型类字面量”错误。通过去除泛型参数并传递具体类型作为参数的方法绕过了这一限制，确保了程序的正确运行。

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出现错误的代码如下：

public class ModServiceFinderImpl<Module> extends BaseFinderImpl<Module> implements ModServiceFinder<Module>{
	public PageView<Module> findByModid(String modid, int pageNo, int pageSize ) {
		PageView<Module> pv = new PageView<Module>();
		if(modid != null && !"".equals(modid)) {
			pv = super.findByPage(Module.class,
					"from Module m where m.isShow=1 and m.parent.mod_id=" + modid, pageNo, pageSize);
		}else {
			pv = super.findByPage(Module.class, "from Module m where m.isShow=1",
					pageNo, pageSize);
		}
		return pv;
	}
}

[color=red]错误信息：Illegal class literal for the type parameter Module[/color]

[color=red]解决方法：将类ModServiceFinderImpl<Module>后的泛型参数去掉[/color]

修改后的代码：

public class ModServiceFinderImpl extends BaseFinderImpl<Module> implements ModServiceFinder<Module>{
	public PageView<Module> findByModid(String modid, int pageNo, int pageSize ) {
		PageView<Module> pv = new PageView<Module>();
		if(modid != null && !"".equals(modid)) {
			pv = super.findByPage(Module.class,
					"from Module m where m.isShow=1 and m.parent.mod_id=" + modid, pageNo, pageSize);
		}else {
			pv = super.findByPage(Module.class, "from Module m where m.isShow=1",
					pageNo, pageSize);
		}
		return pv;
	}
}

总结：这个问题与网络上得另一个问题相同：
问题：Hi all,
I'm creating a generic class and in one of the methods I need to know the Class of the generic type currently in use. The reason is that one of the method's I call expects this as an argument.

Example:
public class MyGenericClass<T> {
  public void doSomething() {
    // Snip...
    // Call to a 3rd party lib
    T bean = (T)someObject.create(T.class);
    // Snip...
  }
}

Clearly the example above doesn't work and results in the following error: Illegal class literal for the type parameter T.
My question is: does someone know a good alternative or workaround for this?

解决方法：
Still the same problems : Generic informations are erased at runtime, it cannot be recovered. A workaround is to pass the class T in parameter of a static method :

public class MyGenericClass<T> {

    private final Class<T> clazz;

    public static <U> MyGenericClass<U> createMyGeneric(Class<U> clazz) {
        return new MyGenericClass<U>(clazz);
    }

    protected MyGenericClass(Class<T> clazz) {
        this.clazz = clazz;
    }

    public void doSomething() {
        T instance = clazz.newInstance();
    }
}