about Downcasting in java

Question

Why this code doesn't work?
https://code.sololearn.com/c94TjAaR7c22/?ref=app

Answer 1

paragraph from stackoverflow:

A non-static nested class in Java contains an implicit reference to an instance of the parent class. Thus to instantiate a Node, you would need to also have an instance of Stack. In a static context (the main method), there is no instance of Stack to refer to. Thus the compiler indicates it can not construct a Node.

If you make Node a static class (or regular outer class), then it will not need a reference to Stack and can be instantiated directly in the static main method.

See the Java Language Specification, Chapter 8 for details, such as Example 8.1.3-2.

[https://stackoverflow.com/questions/13373779/non-static-class-cannot-be-referenced-from-a-static-context]

solution:

declare the nested classes outside your class or make them static