How can i get class from Object parameter?

Question

If i put object of A class as argument of someMeth(Object o), how can i access to this object methods? I cant change or overrdie someMeth(Object o).

...
void someMeth(Object o) {
     o.setS("example"); -- exception : setS() is undefined for type Object
}
...
class A {
    private String s;
    String getS () {
        return s;
    }
    void setS(String value) {
        s = value;
    }

}
...
someMeth(new A());

this is just bad design

MCMastery
– MCMastery

2017-04-16 12:22:15 +00:00
Commented Apr 16, 2017 at 12:22 — MCMastery
– MCMastery, Commented Apr 16, 2017 at 12:22

crow · Accepted Answer · 2017-04-16 12:18:53Z

2

Try casting the object o to they type A like so:

A newObj = (A) o;

Then you can do:

newObj.setS("example");

Or a shorter, one line version:

((A)o).setS("example");

answered Apr 16, 2017 at 12:18

crow

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Comments

Vladimir Parfenov · Accepted Answer · 2017-04-16 12:19:42Z

2

Try to convert type of reference:

void someMeth(Object o) {
     if (o instanceof A) {
         ((A) o).setS("example");
     }
}

answered Apr 16, 2017 at 12:19

Vladimir Parfenov

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2 Comments

nikolay Over a year ago

but you can do that without determinating of o instantiates

Vladimir Parfenov Over a year ago

If your intent is "call concrete method", you determine instance automatically in your mind. If you have several instances, you need to create interface with method setS() and convert o to your interface type. If you'll remove if statement and object won't instance of A you can catch ClassCastException.

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