Iterator
layout: default
title: Iterator Explained
Iterator is a sort of helper object that Set provides.
Set<String> strSet = new HashSet<>();
strSet.add("Ada Lovelace");
strSet.add("Linus Torvalds");
strSet.add("Alan Turing");
strSet.add("Tim Berners-Lee");
strSet.add("Grace Hopper");
Iterator<String> it = strSet.iterator();
We can imagine Iterator like a cursor on a screen that sits at the first element in the collection.
Calling hasNext() says whether the cursor is sitting at an element.
while(it.hasNext()) {
// ...
}
next() returns the element and advances the cursor.
while(it.hasNext()) {
String s = it.next();
// ...
}
Note: we must call next() to advance the cursor, or risk an infinite loop.
while(it.hasNext()) {
System.out.println(it.hasNext()); // Bug: should have called next() here.
// Always true, always prints true.
}