Forcing me to have a parameterless constructor no matter what I do takes this control away from me. How is this different from expecting a parameterless constructor? Well, obviously, a constructor always does at least one thing - it creates an object (or dies trying).īut I like to be in control of how I want my objects to be instantiated. If you define a method setCoordinates(int x, int y), you don't expect compiler to automatically accept a parameterless version of it - setCoordinates(). In the great days of sail, vessels were designed and built on the basis of practical experience ship construction was predominantly a skill. Ship construction today is a complicated compound of art and science. Return new Person() // this will blow in our faceĪll this fuss could be - and is - avoided thanks to the fact that Java (and not only Java) works the way it works. ship construction, complex of activities concerned with the design and fabrication of all marine vehicles. Throw new RuntimeException("Illegal constructor called") īut I still can't forbid another developer to create a method (inside the Person class, so marking the constructor as private didn't help): public static Person createPerson() don't use this constructor! i don't want it to ever be called! This.firstName = null // or "", or whateverĪnd since I don't want it - as it's useless, I might feel inclined to put skull and crossbones on it: Person() You are forcing me to provide another implementation: private Person() An object cant be created in Java without a constructor. If I have a class (that I want to be immutable): class PersonĪnd I add a constructor: Person(String firstName, String lastName)Īnd Java was still to provide a default, parameterless constructor, then this code can't compile, because firstName and lastName fields are declared as final, yet they are not set after you call Person p = new Person(). He is an adjunct professor of computer science and computer programming. Java still generating a parameterless constructor after you define another version of it is like the same waiter taking the coat off you after you gave a clear indication that you have your own plans of what to do with the coat. Java generating a parameterless constructor when you don't have any other is like a polite waiter taking your coat for you. And, this is logically correct since, if you want to block creation of objects without any data in it, this is one good way.įor example, consider that an employee object must have an employee id associated to it.įor achieving this, define a single argument constructor and don't define no-argument constructor. So it will give an error if you call no-argument constructor after defining a parameterised constructor, since it finds no no-argument constructor explicitly defined in class. It's just like authenticating any other method of a class. When you do not explicitly write a no-argument constructor for a class, the compiler won't complain as long as objects are built without parameter constructors.(since compiler allows default constructor to create objects, which itself gives call to no-argument constructor).īut if you do define a no-argument constructor, when compiling, compiler will check for the call to constructor and its definition in class. It is defined like other member functions of the class, i.e.First of all, default constructor is not generated, its provided by compiler if no-argument constructor is not written explicitly. A destructor is called when an object of the class goes out of scope, or when the memory space used by it is de allocated with the help of delete operator. These are used to deinitialize objects when they are destroyed. A constructor (having the same name as that of the class) is a member function which is automatically used to initialize the objects of the class type with legal initial values.ĭestructors are the functions that are complimentary to constructors.
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