Decorator

import java.util.AbstractList;
import java.util.ArrayList;
import java.util.List;


public class OnlyNList extends AbstractList<String> {

    private List<String> decorated ;
    private int n;

    public String get(int i) {
        return decorated.get(i);
    }

    public int size() {
        return decorated.size();
    }

    public OnlyNList(int n, List<String> decorated) {
        this.n = n;
        this.decorated = decorated;
    }

    public String set(int i,String e) {
        if (e.length() > this.n)
            throw new UnsupportedOperationException();
        return this.decorated.set(i,e);
    }

    public void add(int i,String e) {
        if (e.length() > this.n)
            throw new UnsupportedOperationException();
        this.decorated.add(i,e);
    }

    public String remove(int i) {
        return this.decorated.remove(i);
    }

    public static void main(String argv[]) {
        OnlyNList l = new OnlyNList(4, new ArrayList<String>());

        l.add("1234");

        System.out.println(l);

        try {
            l.add("12345");
        } catch (Exception e) {
            System.out.println("OK");
        }

        l.add("abcd");
        l.add("1ab2");
        l.add("xyz0");
        System.out.println(l);


        for(String s: l) System.out.println(s);
    }

}