How to iterate any Map in Java

There are three main ways that you can iterate through a java map

Use entrySet() function

				
					public void iterateByEntrySet(Map<String, Integer> map) {
    for (Map.Entry<String, Integer> entry : map.entrySet()) {
        System.out.println(entry.getKey() + ":" + entry.getValue());
    }
}

2. Use ketSet() function

				
					public void iterateByKeySetAndForeach(Map<String, Integer> map) {
    for (String key : map.keySet()) {
        System.out.println(key + ":" + map.get(key));
    }
}

3. Use Values() function (Iterate over the values regardless of the key)

				
					public void iterateValues(Map<String, Integer> map) {
    for (Integer value : map.values()) {
        System.out.println(value);
    }
}

The followings are some more example operations on java map using java stream API

eg 1: filter map using map value field and build comma separated string.

eg 2: filter map using map key and collect the result to a new map

				
					Map<Integer, String> map = new HashMap<>();
map.put(1, "a");
map.put(2, "b");
	
//filter map using map value field and build comma seperated string.
String result = map.entrySet().stream()
		.filter(x -> "something".equals(x.getValue()))
		.map(x->x.getValue())
		.collect(Collectors.joining());

//filter map using map key and collect the result to a new map
Map<Integer, String> collect = map.entrySet().stream()
		.filter(x -> x.getKey() == 2)
		.collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue()));		

Map<Integer, String> collect = map.entrySet().stream()
		.filter(x -> x.getKey() == 3)
		.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));