User User - 9 days ago 4
Java Question

PMD Overridable method called during object construction

I have the following structure

public class parent {
int value ;
}

public class child extends parent {
int childValue;
public child(){}
public child (int value){
this.childValue = value ; // this line cause ConstructorCallsOverridableMethod warning during object construction
}
}


Could you please advice how to solve this error ?

Answer

The PMD rule says:

Calling overridable methods during construction poses a risk of invoking methods on an incompletely constructed object and can be difficult to debug. It may leave the sub-class unable to construct its superclass or forced to replicate the construction process completely within itself, losing the ability to call super(). If the default constructor contains a call to an overridable method, the subclass may be completely uninstantiable. Note that this includes method calls throughout the control flow graph - i.e., if a constructor Foo() calls a private method bar() that calls a public method buz(), this denotes a problem.

Example:

public class SeniorClass {
  public SeniorClass(){
      toString(); //may throw NullPointerException if overridden
  }
  public String toString(){
    return "IAmSeniorClass";
  }
}
public class JuniorClass extends SeniorClass {
  private String name;
  public JuniorClass(){
    super(); //Automatic call leads to NullPointerException
    name = "JuniorClass";
  }
  public String toString(){
    return name.toUpperCase();
  }
}

Solution

Delete any call to overridable methods in the constructor or add the final modifier to that methods.