Test

package test;

public class SO {

    public static void main(String[] args) {
        for (MyInt mi : new MyInt[]{new PositiveInt(), new EvenInt()}) {
            mi.setMyInt(5);
            System.out.println(mi.getMyInt());
            mi.setMyInt(-6);
            System.out.println(mi.getMyInt());
            mi.setMyInt(0);
            System.out.println(mi.getMyInt());
            System.out.println();
        }
    }
}

    abstract class MyInt {

        private int myInt;

        public int getMyInt() {
            return myInt;
        }

        public void setMyInt(int i) {
            myInt = checkMyInt(i);
        }

        protected abstract int checkMyInt(int i);
    }

//only positive values
class PositiveInt extends MyInt {

    @Override
    protected int checkMyInt(int i) {
        if (i < 0) {
            return -1;
        }
        if (i == 0) {
            return 1;
        }
        return i;
    }
}

//only even values
class EvenInt extends MyInt {

    @Override
    protected int checkMyInt(int i) {
        return 2 * (i / 2);
    }
}