10 November 2019

Different Ways to Iterate Through a Map in Java

development

Looping over a Map in Java. In this post, we look at four different ways we can iterate through a map in Java. As of Java 8, we can use the forEach method as well as the iterator class to loop over a map.

How to Iterate Map Entries (Keys and Values)

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

How to Iterate Map Keys Only

Map<Integer, Integer> map = new HashMap<Integer, Integer>();

for (Integer key : map.keySet()) {
    System.out.println("Key = " + key);
}

How to Iterate Map Values Only

for (Integer value : map.values()) {
    System.out.println("Value = " + value);
}

How to loop through an ArrayLists in Java

Using Iterator

Using Generics:

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();
while (entries.hasNext()) {
    Map.Entry<Integer, Integer> entry = entries.next();
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

Without Generics:

Map map = new HashMap();
Iterator entries = map.entrySet().iterator();
while (entries.hasNext()) {
    Map.Entry entry = (Map.Entry) entries.next();
    Integer key = (Integer)entry.getKey();
    Integer value = (Integer)entry.getValue();
    System.out.println("Key = " + key + ", Value = " + value);
}

Iterating over keys and searching for values

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (Integer key : map.keySet()) {
    Integer value = map.get(key);
    System.out.println("Key = " + key + ", Value = " + value);
}

Using Java 8 ForEach

Map<String, Integer> items = new HashMap<>();
    items.put("key 1", 1);
    items.put("key 2", 2);
    items.put("key 3", 3);

    items.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));

10 November 2019