Proper way to achieve inheritance

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I have this abstract class: FooAbstract, and two classes extending it: FooSingleInstance and FooMultiInstances.

public abstract class FooAbstract{
    private boolean single;
    public FooAbstract(boolean single){
        this.single = single;
    }

    public boolean isSingle(){
        return single;
    }
}

public class FooSingleInstance extends FooAbstract{
        public FooSingleInstance(boolean single){
            super(single);
        }
        private Bar bar;
        public Bar getBar(){
            return bar;
        }
    }
public class FooMultiInstances extends FooAbstract{
        public FooMultiInstances(boolean single){
            super(single);
        }
        private Map<String, Bar> barMap;
        public Bar getBarFromKey(String key){
            return barMap.get(key);
        }
    }

And I have a method doSomethingWithBar(FooAbstract foo):

public void doSomethingWithBar(FooAbstract foo){
    if(foo.isSingle()){
        Bar bar=((FooSingleInstance) foo).getBar();
        //do something with bar
    }else{
        //some logic to get key
        Bar bar=((FooMultiInstances) foo).getBarFromKey(key);
        //do something with bar
    }
}

The code kind of achieves what I was intended to achieve, but I don't feel it is adhering to coding principles. Is there a better way to achieve this?

asked 25 secs ago

santosh-patil

791

Proper way to achieve inheritance