问题
In java, An outer class may be public, final, default or abstract. Why not Static like
public static class MyClass{}
回答1:
An outer class is already implicitly static.
Non-static nested class (= inner class) means thats the inner class implicitly has a reference to its parent class.
That's why, for nested class, you can distinguish between static and non-static. This does not make sense for outer classes.
Here is an example to understand the difference between static/non-static nested class. You should understand why it does not make sense in an outer class.
public class MyClass {
private String anAttributeOfMyClass;
private /*static*/ class MyInnerClass {
public void foo() {
/*
* Here, I can access the attribute of the parent class
* because I implicitly have a reference to it.
* Try to make the nested class static an see the difference.
*/
anAttributeOfMyClass.trim();
}
}
}
来源：https://stackoverflow.com/questions/18738049/why-outer-classes-are-not-static-in-java