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Editorial Team
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Asked: 2026-05-26T05:31:49+00:00

I have a doubt about using the constructor to initialize lists and other fields

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I have a doubt about using the constructor to initialize lists and other fields when using JPA, specifically my question is as follows:

Suppose I have an entity bean, that has lots of @OneToMany relationships, I would like to use the constructor to initialize them, so that I don’t have to use statements like this in my controllers:

myEntity=new MyEntity();
myEntity.innerList=new ArrayList<Type>();
myEntity.innerList.add(newObject);

so instead I would have:

public MyEntity(){
 innerList=new ArrayList<Type>();
}

Now, the question is… will JPA call this constructor when mapping properties from the database?. I mean If I had persisted before an entire list, will the constructor run and reinitialize my entites lists?. Thanks a lot.

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1 Answer

  1. Editorial Team

    Yes, JPA will call the no-arg constructor of your entity. After that, your lists will be replaced by specific List implementations of your JPA engine. These lists allow lazy-loading and other functionalities needed by the JPA engine.

    I wouldn’t care much about the needless ArrayList instantiation in this case. This is not where a typical JPA application will take the most time. I find it much more important to have clear invariants and to respect them. One of these invariants is : my entity always has a non-null list of other entities.

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