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Java Collections Iteration

Two iterator patterns can be used with collections. The first is a simple iteration through all elements:

for ( AnyType item : coll )

The second form allows more complicated processing, including removal of an item.

Iterator<AnyType> itr = coll.iterator();

while ( itr.hasNext() ) {
  AnyType item =;
  ...          // process item
  if ( ... )   itr.remove();   }
In this pattern, an iterator object itr is created. This object can be queried to test whether any items remain using itr.hasNext(). If there are objects, gets the next one. itr.remove() removes the last object returned by and can only be used once until there is another call to .

A collection should not be modified while an iteration over it is in progress, except by the itr.remove() .