How Do I Preserve Insertion Order in Java HashMaps?

Preserving Insertion Order in HashMaps

When working with HashMaps, it's common to encounter situations where the order of elements during iteration is inconsistent with their insertion order. However, in certain use cases, maintaining the insertion order is crucial. To address this need, the Java Collections Framework provides the LinkedHashMap.

Solution: LinkedHashMap

The LinkedHashMap class extends the HashMap class. It retains the insertion order by maintaining an internal doubly-linked list that connects the elements in the order they are inserted. When iterating over a LinkedHashMap, the elements are returned in the same order in which they were added.

Example:

<code class="java">Map<Integer, String> map = new LinkedHashMap<>();
map.put(1, "One");
map.put(3, "Three");
map.put(2, "Two");

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

Output:

1: One
3: Three
2: Two

As you can see, the elements are printed in the order they were inserted (1, 3, 2).

Conclusion:

By utilizing LinkedHashMap, you can preserve the insertion order of elements in a HashMap. This feature is particularly useful for scenarios where the order of the elements is critical for the correct operation of your application.

The above is the detailed content of How Do I Preserve Insertion Order in Java HashMaps?. For more information, please follow other related articles on the PHP Chinese website!