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By convention, the returned object should be obtained by calling super.clone. If a class and all of its superclasses (except Object) obey this convention, it will be the case that x.clone().getClass() == x.getClass().

Noncompliant Code Example

In this noncompliant code example, the clone() method in the class Base fails to call super.clone():

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Consequently, the object devClone ends up being of type Base instead of Derived and the doLogic() method is incorrectly applied.

Compliant Solution

This compliant solution correctly calls super.clone() in the Base class's clone() method:

class Base implements Cloneable {
  public Object clone() throws CloneNotSupportedException {
    return super.clone();	 
  }
  protected void doLogic() {
    System.out.println("Superclass doLogic");
  }
}

class Derived extends Base {
  public Object clone() throws CloneNotSupportedException {
    return super.clone();
  }
  protected void doLogic() {
    System.out.println("Subclass doLogic");
  }
  public static void main(String[] args) {
    Derived dev = new Derived();
    try {
      Base devClone = (Base)dev.clone(); // Has type Derived, as expected
      devClone.doLogic();  // Prints "Subclass doLogic", as expected
    } catch (CloneNotSupportedException e) { /* ... */ }
  }
}

Applicability

Failing to call super.clone() may cause a cloned object to have the wrong type, with unexpected or incorrect results when it is used.

Bibliography

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