Explanation how super () method works in Java
I have a problem with the super method but I don't really know what to do to make it work. Help!
public class ClassUno {
public static void main(String[] args) {
}
///// Clases Internas ////
class Primera {
int k;
public Primera( int s ) {
k = s;
}
}
class Segunda extends Primera {
public Segunda() {
super();
}
public Segunda( int n ) {
k = n;
}
}
}
2 answers
When using inheritance in Java, in Constructors you declare in child classes they should always call super(args) or this(args), where:
-
super(args)refers to a constructor of the parent class. -
this(args)refers to a constructor defined in the current class. -
argsinsuper(args)andthis(args)refers to the possible arguments required by the constructor being called.
Note that in Constructors of a class child, at least one constructor must call super() and the other constructors can call super() or this().
This is explained in the Java specification, Chapter 8 classes, part 8.8 Constructor declarations, section 8.8.7 Constructor body .
Knowing this, let's look at the definition of Primera:
class Primera {
int k;
public Primera(int s) {
k = s;
}
}
It can be observed that there is only 1 constructor that receives 1 argument of type int. Now let's look at the constructors of Segunda:
class Segunda extends Primera {
public Segunda() {
/*
error de compilación
Causa: No existe un constructor en la clase padre
sin argumentos
*/
super();
}
public Segunda( int n ) {
/*
error de compilación
Causa: no se llama a super(args) o this(args) en la primera línea
*/
k = n;
}
}
This can have multiple solutions depending on the design of your classes. Here is an example:
class Segunda extends Primera {
public Segunda() {
/*
se llama al constructor Segunda(int)
y se envía como argumento 0
*/
this(0);
}
public Segunda( int n ) {
/*
se llama al constructor de la clase padre
con argumento n. En la clase padre, va a inicializar
el valor del campo k con el valor de la variable n
*/
super(n);
}
}
I would think that your problem is that when you put the super you have to pass as a parameter the attributes it has in the first class. In your case it is the variable "s". Then you would look like this:
public static void main(String[] args) {
}
Internal Classes
class Primera {
int k;
public Primera( int s ) {
k = s;
}
}
class Segunda extends Primera {
// aca es donde le pasas por parametro la variable s. si tuvieras mas variables deberias de pasarle todas las variables como parametro
public Segunda() {
super(s);
}
public Segunda( int n ) {
k = n;
}
}