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 Child(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());
}
}
