java function - print(collection c) ?

Question

Hi. I'm trying to learn java better and I got one question.

Say I got two collections, an ArrayList and a LinkedHashSet. Is it possible to make a function like this:

void print(collection c) {
    for (object tmp:c) {
        System.out.println(tmp);
    }
}

Answer 1

Watch your capitalization:

private void printCollection(Collection collection) {

   for (Object obj : collection) {
      System.out.println(obj);
   }
}

Answer 2

Yes. ArrayList and LinkedHashSet are both Collections. The method that you wrote accepts a Collection (note the capital C) so it will accept any type of collection. This is referred to as polymorphism.

Answer 3

basically you just need ot use the iterator:

void print(collection c) 
{ 
    for (object tmp:c.iterator()) 
    { 
        System.out.println(tmp); 
    } 
} 

Answer 4

It is possible, as both types implement Collection<E>. The convention is for class types in Java to start with a capital letter. Since 1.5, Java has used generics for its collections and you should use them in all new code. Since you're using the 1.5 style for loop, you should write generic code.

It's usually better to make functions operate on the least specific type as possible, as this gives the widest reuse. In this case, you only need something wich could go one up from Collection<T> to Iterable<T>, as you only need something which will work with the for loop. So combining generics and least power gives:

public class PrintLinePrinter {
    public <T> void print (Iterable<T> collection) { 
        for (T item : collection) {
            System.out.println(item); 
        }
    } 
} 

Answer 5

System.out.println(Collection c) already print any type of collection in readable format. But if collection contains user defined objects , then you need to implement toString() in user defined class.

Answer 6

'Loop free' solution:

void print(collection c) {
    System.out.println( Arrays.toString(c.toArray())); }