getClass（）返回null但Foo.class工作

Question

When using the following I get a NullPointerException :

Class clazz = Foo.class;
String path = new File(clazz.getClass().getProtectionDomain().getCodeSource().getLocation().toURI().getPath()) + "";

However, it works when I use:

String path = new File(Foo.class.getProtectionDomain().getCodeSource().getLocation().toURI().getPath()) + "";

Is there any way around the NullPointerException ?

Answer 1

You should call getClass() on an instance of a class.

MyClass myClassInstance = new MyClass();
Class clazz = myClassInstance.getClass();

You are trying to call it on the class Object

Answer 2

You don't have to invoke getClass on your clazz or you will get the Class.class instead of Foo.class.

So it should be:

Class clazz = Foo.class;
String path = new File(clazz.getProtectionDomain().getCodeSource().getLocation().toURI().getPath()) + "";

Answer 3

It depends on how the class was loaded - like for instance if the class was loaded from the Bootstrap classloader .

See here for a more complete answer.