CrackingCodingInterview. Implement Stack with LinkedList

StackList.java

class StackList {
    Node top;

    void push(Object data){
        Node t = new Node(data);
        t.next = top;
        top = t;
    }

    Object pop(){
        if(top == null){
            return null;
        }else{
            Object item = top.data;
            top = top.next;
            return item;
        }
    }

    Object peek(){
        if(top == null){
            return null;
        }
        return top.data;
    }
}