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Invocation of an overridable method during object construction may result in the use of uninitialized data, leading to runtime exceptions or to unanticipated outcomes. Calling overridable methods from constructors can also leak the this reference before object construction is complete, potentially exposing uninitialized or inconsistent data to other threads (see TSM01-J. Do not let the this reference escape during object construction for additional information). As a result, constructors a class's constructor must invoke (directly or indirectly) only methods in that class that are static, final or private.

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class SuperClass {
  public SuperClass () {
    doLogic();
  }

  public void doLogic() {
    System.out.println("This is superclass!");
  }
}

class SubClass extends SuperClass {
  private String color = null;
  public SubClass() {
    super();
    color = "Red"red";
  }

  public void doLogic() {
    System.out.println("This is subclass! The color is :" + color);
    // ...
  }
}

public class Overridable {
  public static void main(String[] args) {
    SuperClass bc = new SuperClass();
    // Prints "This is superclass!"
    SuperClass sc = new SubClass();
    // Prints "This is subclass! The color is :null"
  }
}

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Allowing a constructor to call overridable methods can provide an attacker with access to the this reference before an object is fully initialized, which could lead to a vulnerability.

Automated Detection

Automated detection of constructors that contain invocations of overridable methods is straightforward.

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Related Guidelines

Bibliography

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