The recommended approach is to use static inner classes, if you must use an inner class at all.

推荐的做法是如果非要使用内部类的话，请使用静态内部类。

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Referring to enclosing type parameters inside static methods and static inner classes is prohibited outright by the compiler. So, for instance, the following code is illegal in tiger.

编译器完全禁止在静态方法和静态内部类中引用封闭类型参数。

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Referring to enclosing type parameters inside static methods and static inner classes is prohibited outright by the compiler. So, for instance, the following code is illegal in tiger.

编译器完全禁止在静态方法和静态内部类中引用封闭类型参数。

youdao