How to Iterate Map in Java
January 31, 2022
Map in following ways.
1. Use
Map.entrySet that returns a collection view of Map.Entry.
2. Iterate over
Map.entrySet using Iterator.
3. Iterate over
Map.keySet for keys
4. Iterate over
Map.values for values.
5. Iterate map using
Map.forEach method.
Now let us discuss iterating
Map with examples.
Contents
Using Map.Entry and Map.entrySet
TheMap.Entry represents a key-value pair. The Map.entrySet returns a collection view of Map.Entry.
Set<Entry<Integer, String>> entrySet = map.entrySet();
HashMap that we will iterate.
Map<Integer, String> map = new HashMap<Integer, String>(); map.put(1, "Mahesh"); map.put(2, "Suresh"); map.put(3, "Nilesh");
Map using Map.Entry and Map.entrySet.
Set<Entry<Integer, String>> entrySet = map.entrySet();
for (Map.Entry<Integer, String> mapEntry : entrySet) {
System.out.println(mapEntry.getKey() + " " + mapEntry.getValue());
}
1 Mahesh 2 Suresh 3 Nilesh
Using Iterator and Map.entrySet
TheIterator iterates over a collection.
Iterator<Map.Entry<Integer, String>> mapEntryIte = map.entrySet().iterator();
while (mapEntryIte.hasNext()) {
Entry<Integer, String> entry = mapEntryIte.next();
System.out.println(entry.getKey() + " " + entry.getValue());
}
Using Map.keySet and Map.values
Map.keySetSet<K> keySet()
Set of keys contained in this map.
Iterate over keys.
for (Integer key : map.keySet()) {
System.out.println(key + " " + map.get(key));
}
Map.values
Collection<V> values()
Collection of the values contained in this map.
Iterate over values.
for (String v : map.values()) {
System.out.println(v);
}
Using forEach
TheMap interface provides forEach as default method. The forEach method accepts BiConsumer as argument.
map.forEach((k,v) -> System.out.println(k +" : "+ v));
1 : Mahesh 2 : Suresh 3 : Nilesh
Iterate with var
The var keyword is the local variable type inference. It reduces the boilerplate code. With type inference, compiler can figure out the static types and we don’t have to write them.
for (var entry : map.entrySet()) {
var key = entry.getKey();
var value = entry.getValue();
System.out.println(key + ": " + value);
}
