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Wiki MarkupIncreasing the accessibility of overridden or hidden methods permits a malicious subclass to offer wider access to the restricted method than was originally intended. Consequently, programs must override methods only when necessary and must declare methods final whenever possible to prevent malicious subclassing. When methods cannot be declared final, programs should refrain from increasing the accessibility of overridden methods. See rule SEC01-J for more information.)

 intended. The access modifier of an overriding or hiding method must provide at least as much access as the overridden or hidden method \[[JLS 2005|AA. Bibliography#JLS 05](_Java Language Specification_, §8.4.8.3, "Requirements in Overriding and Hiding"\] \[[JLS 2005|AA. Bibliography#JLS 05]. The following are the allowed accesses:

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This noncompliant code example demonstrates how a malicious subclass Sub can both override the doLogic() method of the superclass and also increase the accessibility of the overriding method. Any user of Sub can invoke the doLogic method because the base class BadScope Super defines it to be protected. Class Sub increases , consequently allowing class Sub to increase the accessibility of doLogic() by declaring its own version of the method to be public.

class BadScopeSuper {
  protected void doLogic() {
    System.out.println("Super invoked");
  }
}

public class Sub extends BadScopeSuper {
  public void doLogic() {
    System.out.println("Sub invoked");
    // Do sensitive operations
  }
}

Compliant Solution

Override methods only when necessary. Declare methods and fields final whenever possible to avoid malicious subclassing. When methods and fields cannot be declared final, refrain from increasing the accessibility of overridden methods. (See OBJ02-J. Minimize the accessibility of classes and their members.)This compliant solution declares the doLogic() method final to prevent malicious overriding.

class BadScopeSuper {
  protected final void doLogic() { // declare as final
    System.out.println("Super invoked");
    // Do sensitive operations
  }
}

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Related Guidelines

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