class Logger {
    static /*@non_null @*/ List theList = new List();

    public static void log(String msg) {
	System.err.println("Log "+msg+": state of list is "+theList);
    }
}

public class List {
    private /*@ non_null @*/ int[] content = new int[0];
    private int size;
    /*@ private invariant 0 <= size && size <= content.length; @*/

    public void add(int v) {
	size++;
	if (size > content.length) {
	    Logger.log("growing content");
	    int[] newContent = new int[2*size];
	    System.arraycopy(content, 0, newContent, 0, content.length);
	    content = newContent;
	}
	content[size-1] = v;
    }

    //@ private ghost String myString; in privateState;
    //@ private represents theString <- myString;

    public String toString() {
	String s = "[";
	String comma ="";
	for (int i = 0; i < size; i++) {
	    s += comma + content[i];
	    comma = ",";
	}
	s += "]";
	//@ set myString = s;
	return s;
    }

    public static void main(String[] param) {
	List list = Logger.theList;
	list.add(5);
    }
}