public void borrowBooks(String id, String name, String sid, String sname) {
	if((getKeyFromValue(Books, name).equals(id))&&(getKeyFromValue(Students, sname).equals(sid))){
		if((Object)Library.countValues(sid)!=5){
			Library.put(id, sid);
		}
		else{
			System.out.println("You have exceeded your quota. Return a book before you take one out." );
		}
	}
}

if (Library.get(id) == null) {
   Library.put(id, new ArrayList<String>());
}
List<String> books = Library.get(id);
int number = books.size() // gives you the size

if(((Object)Library).countValues(sid) != 5)

initialize count to 0
for each entry in Library:
    if the value is what you want:
        increment the count

int count = 0;

for(String str : Library.values())
{
    if(str == sid)
        count++;
    if(count == 5)
        break;
}

if(count < 5)
    Library.put(id, sid);
else
    System.out.println("You have exceeded your quota. Return a book before you take one out." );