public class Node {
    private int inf;
    private Node next;

    Node() {
        inf=0;
        next=null;
    }
    Node(int i) {
        inf=i;
        next=null;
    }

    public void setInf(int i) {
        inf=i;
    }
    public void setNext(Node n) {
        next=n;
    }

    public int getInf() {
        return inf;
    }
    public Node getNext() {
        return next;
    }
}

public class List {
    private Node first;
    List() {
        first=null;
    }

    public void addFirstNode(Node n) {
        n.setNext(first);
        first=n;
    }

    public void addLastNode(Node n) {
        if (first==null) first=n;
        else {
            Node tmp=first;
            while (tmp.getNext()!=null) {
                tmp=tmp.getNext();
            }

            tmp.setNext(n);
        }
    }
    public void addFirst(int a) {
        Node newnode = new Node(a);
        addFirstNode(newnode);
    }

    public void addLast(int a) {
        Node newnode = new Node(a);
        addLastNode(newnode);
    }

    public void showList() {
        Node tmp=first;
        while (tmp!=null) {
            System.out.print(" "+tmp.getInf());
            tmp=tmp.getNext();
        }
        System.out.println();
    }

}

package dom;

//основная программа

public class Dom {

    public static void main(String[] args) {
        List queue = new List();
        List stack = new List();

        String s = "125478965321547896521547889633215478965487512546985478521";

        int l = s.length();
        for (int i=0; i<l; i++) {
            if (i%2==0)
            {   char k=s.charAt(i);
                queue.addLast(k);
            }
            if (i%5==0)
            {   char k=s.charAt(i);
                stack.addFirst(k);
            }
        }

        queue.showList();
        stack.showList();
    }
}

System.out.print(" " + (char)tmp.getInf());

public void showList() {
        Node tmp=first;
        while (tmp!=null) {
            System.out.print(" "+ (char)tmp.getInf()); //здесь преобразование кода в символ
            tmp=tmp.getNext();
        }
        System.out.println();
    }

//Node
private Object inf;
Node(Object inf){
    this.inf = inf;
    next = null;
}
public void setInf(Object inf){
    this.inf = inf;
}
public Object getInf(){
    return inf;
}

//List
public void addFirst(Object inf){
    Node newnode = new Node(inf);
    addFirstNode(newnode);
}
public void addLast(Object inf){
    Node newnode = new Node(inf);
    addLastNode(newnode);
}