What will happen if we dont have no-arg constructor in Entity Bean?

For fields with constraints, such as @NonNull fields, no check is generated,so be aware that these constraints will generally not be fulfilled until those fields are properly initialized later. Certain java constructs, such as hibernate and the Service Provider Interface require a no-args constructor .

If you don’t define any constructors, the compiler will generate the default one , as described in the JLS: If a class contains no constructor declarations, then a default constructor with no formal parameters and no throws clause is implicitly declared.

All classes have at least one constructor . If a class does not explicitly declare any, the Java compiler automatically provides a no-argument constructor, called the default constructor.

No-Arg Constructor – a constructor that does not accept any arguments . Parameterized constructor – a constructor that accepts arguments. Default Constructor – a constructor that is automatically created by the Java compiler if it is not explicitly defined.