Java collection framework has Map interface and several implementation classes like HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap. Map one of the most used interface used to store and operate on key-value pairs.
To iterate all entries of a Map, there are several ways as given below.
1- Using foreach and entrySet method
for (Map.Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
2- Using map.forEach method
map.forEach((key, value) -> {
System.out.println(key);
System.out.println(value);
});
3- Using Iterator and Map.Entry with while loop
Iterator<Map.Entry<String, Integer>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, Integer> entry = it.next();
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
4- You iterate on the basis of the keyset only Using keySet and foreach
for (String key : map.keySet()) {
System.out.println(key);
System.out.println(map.get(key));
}
5- You iterate on the basis of the keyset only Using keySet and while loop and iterator
Iterator<String> itr = map.keySet().iterator();
while (itr.hasNext()) {
String key = itr.next();
System.out.println(key);
System.out.println(map.get(key));
}
6- Using for and Map.Entry
for (Iterator<Map.Entry<String, Integer>> entries = map.entrySet().iterator(); entries.hasNext(); ) {
Map.Entry<String, Integer> entry = entries.next();
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
7- Using Java 8 stream
map.entrySet().stream().forEach(e -> {
System.out.println(e.getKey());
System.out.println(e.getValue());
});
8- Using Java 8 stream parrellel
map.entrySet().stream().parallel().forEach(e -> {
System.out.println(e.getKey());
System.out.println(e.getValue());
});