Java Language Collections Iterating over Collections
Example
Iterating over List
List<String> names = new ArrayList<>(Arrays.asList("Clementine", "Duran", "Mike"));
Java SE 8
names.forEach(System.out::println);
If we need parallelism use
names.parallelStream().forEach(System.out::println);
Java SE 5
for (String name : names) {
System.out.println(name);
}
Java SE 5
for (int i = 0; i < names.size(); i++) {
System.out.println(names.get(i));
}
Java SE 1.2
//Creates ListIterator which supports both forward as well as backward traversel
ListIterator<String> listIterator = names.listIterator();
//Iterates list in forward direction
while(listIterator.hasNext()){
System.out.println(listIterator.next());
}
//Iterates list in backward direction once reaches the last element from above iterator in forward direction
while(listIterator.hasPrevious()){
System.out.println(listIterator.previous());
}
Iterating over Set
Set<String> names = new HashSet<>(Arrays.asList("Clementine", "Duran", "Mike"));
Java SE 8
names.forEach(System.out::println);
Java SE 5
for (Iterator<String> iterator = names.iterator(); iterator.hasNext(); ) {
System.out.println(iterator.next());
}
for (String name : names) {
System.out.println(name);
}
Java SE 5
Iterator iterator = names.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
Iterating over Map
Map<Integer, String> names = new HashMap<>();
names.put(1, "Clementine");
names.put(2, "Duran");
names.put(3, "Mike");
Java SE 8
names.forEach((key, value) -> System.out.println("Key: " + key + " Value: " + value));
Java SE 5
for (Map.Entry<Integer, String> entry : names.entrySet()) {
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
// Iterating over only keys
for (Integer key : names.keySet()) {
System.out.println(key);
}
// Iterating over only values
for (String value : names.values()) {
System.out.println(value);
}
Java SE 5
Iterator entries = names.entrySet().iterator();
while (entries.hasNext()) {
Map.Entry entry = (Map.Entry) entries.next();
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
