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Calling an overridable method from a constructor could result in failures or strange behaviors when instantiating a subclass which overrides the method.

For example:

The subclass class constructor starts by contract by calling the parent class constructor.
The parent class constructor calls the method, which has been overridden in the child class.
If the behavior of the child class method depends on fields that are initialized in the child class constructor, unexpected behavior (like a NullPointerException) can result, because the fields aren't initialized yet.


Noncompliant Code Example
public class Parent {

  public Parent () {
    doSomething();  // Noncompliant
  }

  public void doSomething () {  // not final; can be overridden
    ...
  }
}

public class Child extends Parent {

  private String foo;

  public Parent(String foo) {
    super(); // leads to call doSomething() in Parent constructor which triggers a NullPointerException as foo has not yet been initialized
    this.foo = foo;
  }

  public void doSomething () {
    System.out.println(this.foo.length());
  }

}