Q:

cannot find symbol Serializable?

Why does this:
package com.example;

import com.example.Foo.Bar.Baz;

import java.io.Serializable; // I did import Serializable...

public class Foo implements Serializable {

    public final Bar bar;

    public Foo(Bar bar) {
        this.bar = bar == null ? new Bar(Baz.ONE) : bar;
    }

    public static class Bar implements Serializable { // this is line 15, where the compiler error is pointing 

        public enum Baz {
            ONE
        }

        public final Baz baz;

        public Bar(Baz baz) {
            this.baz = baz;
        }
    }

}

Give me this:
[ERROR] <path to file>/Foo.java:[15,44] cannot find symbol
[ERROR] symbol:   class Serializable
[ERROR] location: class com.example.Foo

If I replace the Serializable interface to something else like :
public interface MyMarkerInterface {}

then the code compiles. (even Cloneable works!)
What makes this happen?
intelliJ didn't spot anything wrong through static analysis. 

A:

Don't try and import the internal class. That's causing your compiler error
// import com.example.Foo.Bar.Baz;
import java.io.Serializable;

public class Foo implements Serializable {
    public final Bar bar;

    public Foo(Bar bar) {
        this.bar = bar == null ? new Bar(Bar.Baz.ONE) : bar;
    }

    public static class Bar implements Serializable {
        public enum Baz {
            ONE
        }
        public final Baz baz;
        public Bar(Baz baz) {
            this.baz = baz;
        }
    }
}

