How to implement access restriction to package components so that internal elements remain accessible within the package but are hidden from the outside world?

In Java, the default access modifier (package-private), which means the absence of an explicit public, protected, or private modifier, is used to restrict access to internal package elements.

If a class, method, or field is declared without an access modifier, it is only accessible within the current package and not outside. This allows hiding implementation details while still providing access to other classes within the package.

Example:

// Internal class without an access modifier
class InternalHelper {
    void doSomething() {
        // accessible within the package
    }
}

public class PublicAPI {
    // public class accessible from outside
}

Thus, to hide elements from the outside world, simply do not specify the public modifier, and they will only be accessible within the package.