public abstract class Parent{
    public Parent(){
    }
}

public class ChildA extends Parent {
    public ChildA {
    }
}

public class ChildB extends Parent {
    public ChildB {
    }
}

ChildA child = obj as ChildA;

ChildA child = (ChildA)obj;

ChildA child = (obj instanceof ChildA ? (ChildA)obj : null);

if(obj instanceof ChildA){
     final ChildA child = (ChildA) obj;
}

if (child instanceof ChildA) {
    ChildA child = (ChildA) child;
    // Do stuff.
}

public ChildA getInstance(Parent p) {
    if (child instanceof ChildA) {
        return (ChildA) p;
    } else {
        return null;
    }
}

Object o = new Integer(1);

    Optional.ofNullable(o)
            .filter(Number.class::isInstance)
            .map(Number.class::cast)
            .ifPresent(n -> System.out.print("o is a number"));