Java HashMap key value storage and retrieval

Question

I want to store values and retrieve them from a Java HashMap.

This is what I have so far:

public void processHashMap()
{
    HashMap hm = new HashMap();
    hm.put(1,"godric gryfindor");
    hm.put(2,"helga hufflepuff"); 
    hm.put(3,"rowena ravenclaw");
    hm.put(4,"salazaar slytherin");
}

I want to retrieve all Keys and Values from the HashMap as a Java Collection or utility set (for example LinkedList).

I know I can get the value if I know the key, like this:

hm.get(1);

Is there a way to retrieve key values as a list?

Answer 1

I use these three ways to iterate a map. All methods (keySet, values, entrySet) return a collection.

// Given the following map
Map<KeyClass, ValueClass> myMap;

// Iterate all keys
for (KeyClass key  : myMap.keySet()) 
    System.out.println(key);

// Iterate all values
for (ValueClass value  : myMap.values()) 
    System.out.println(value);

// Iterate all key/value pairs
for (Entry<KeyClass, ValueClass> entry  : myMap.entrySet()) 
    System.out.println(entry.getKey() + " - " + entry.getValue());

Since Java 8 i often use Streams with lambda expressions.

    // Iterate all keys
    myMap.keySet().stream().forEach(key -> System.out.println(key));

    // Iterate all values
    myMap.values().parallelStream().forEach(value -> System.out.println(value));

    // Iterate all key/value pairs
    myMap.entrySet().stream().forEach(entry -> System.out.println(entry.getKey() + " - " + entry.getValue()));