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The readObject() method must not call any overridable methods. Invoking overridable methods from the readObject() method can allow provide the overriding method with access to read the object's state of the subclass before it is fully constructed because the base class is deserialized first, followed by the subclass. As a result, readObject() must not call any overridable methods.Also see the related rule initialized. This premature access is possible because, in deserialization, readObject plays the role of object constructor and therefore object initialization is not complete until readObject exits (see also MET06-J. Do not invoke overridable methods in clone()).

Noncompliant Code Example

This noncompliant code example invokes an overridable method from the readObject() method. :

private void readObject(final ObjectInputStream stream)
                        throws IOException, ClassNotFoundException {
  overridableMethod(); 
  stream.defaultReadObject();
}

public void overridableMethod() {
  // ...
}

...

This compliant solution removes the call to the overridable method. When removing such calls is infeasible, declare the method private or final.

private void readObject(final ObjectInputStream stream)
                        throws IOException, ClassNotFoundException {
  stream.defaultReadObject();
}

Exceptions

Wiki Markup*SER09SER09-J-EX0:* The {{readObject()}} method may invoke the overridable methods {{defaultReadObject()}} and {{readFields()}} in class {{java.io.ObjectInputStream}} \ [[SCG 2009|AA. References#SCG 09]\].

Risk Assessment

Invoking overridable methods from the readObject() method can lead to initialization errors.

Automated Detection

Related Guidelines

Bibliography

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Image Added Image Added Image Removed      13. Serialization (SER)