迭代集合

迭代列表

List<String> names  = new ArrayList<>(Arrays.asList("Clementine", "Duran", "Mike"));

Version => Java SE 8

names.forEach(System.out::println);

如果我们需要并行使用

names.parallelStream().forEach(System.out::println);

Version => Java SE 5

for (String name : names) {
    System.out.println(name);
}

Version < Java SE 5

for (int i = 0; i < names.size(); i++) {
    System.out.println(names.get(i));
}

Version => 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());
}

迭代 Set

Set<String> names = new HashSet<>(Arrays.asList("Clementine", "Duran", "Mike"));

Version => Java SE 8

names.forEach(System.out::println);

Version => Java SE 5

for (Iterator<String> iterator = names.iterator(); iterator.hasNext(); ) {
    System.out.println(iterator.next());
}

for (String name : names) {
    System.out.println(name);
}

Version < Java SE 5

Iterator iterator = names.iterator();
while (iterator.hasNext()) {
    System.out.println(iterator.next());
}

迭代地图

Map<Integer, String> names = new HashMap<>();
names.put(1, "Clementine");
names.put(2, "Duran");
names.put(3, "Mike");

Version => Java SE 8

names.forEach((key, value) -> System.out.println("Key: " + key + " Value: " + value));

Version => 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);
}

Version < 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());
}