'Serializable' object implicitly stores non-'Serializable' object

Reports any references to local non-Serializable variables outside Serializable lambdas, local and anonymous classes.

When a local variable is referenced from an anonymous class, its value is stored in an implicit field of that class. The same happens for local classes and lambdas. If the variable is of a non-Serializable type, serialization will fail.

Example:

interface A extends Serializable {
    abstract void foo();
}
class B {}
class C {
    void foo() {
        B b = new B();
        A a = new A() {
            @Override
            public void foo() {
                System.out.println(b); // warning
            }
        };
    }
}