使用自定义类加载器加载Java运行时和API类

Question

Why is it advisable to load the Java Runtime classes and API classes using the default system class loader in Java? What happens if we load them using our custom class loader?

Answer 1

One of the criterias for instanceof to be true, is that the two classes must be loaded by the same classloader. This goes for class casting too.

This would mean that instances of eg String created by your class loader would not be compatible with the String created by the system class loader. Are not instances of and cannot be cast to.

You probably do not want that.