Setter in constructor

[Dipke]

Hello,

When i write a class in BleuJ with setters in the constructor there is no error or warning.
When i copy this into netbeans, there is a warning.
I have to make the class or the setter final.
What is the reason for that ?

public Name(String name) {
this.name = name; }

or

public Name(String name) {
setName(name); }

[JosAH]

Hello,

When i write a class in BleuJ with setters in the constructor there is no error or warning.
When i copy this into netbeans, there is a warning.
I have to make the class or the setter final.
What is the reason for that ?

public Name(String name) {
this.name = name; }

or

public Name(String name) {
setName(name); }

If you don't make that class final and don't make the setName( ... ) method private or final someone else is able to extend your class and overrid the setName( ... ) method. Your constructor (in your base class) will call that method in the extending class instead of your implementation. Nobody knows what that method can do; hence the warning ... As a rule of thumb: a constructor shouldn't call methods that can be overriden.

kind regards,

Jos

[pbrockway2]

The method in the extending class will be called before the instance has had a chance to initialise itself. If the extending class's method depends on some initialisation your constructor will defeat that and possibly cause grief.

class Base {
    double value;

    Base(double value) {
        this.value = value;
        report();
    }

    void report() {
        System.out.println("Value is " + value);
    }
}

class Ext extends Base {
    int div = 1000;

    Ext(double value) {
        super(value);
    }

    void report() {
        // this looks innocent enough, but the beahviour
        // is a little counterintuitive
        System.out.println("Value in kilounits is " + (value / div));
    }
}

public class Test {
    public static void main(String args[]) {
        Ext test = new Ext(12345);
    }
}

[Dipke]

Thanks for the clear explanation.
It make sense.

Kind regards