How to Preserve Insertion Order in HashMaps in Java?

Preserving Insertion Order in HashMaps using LinkedHashMap

When working with HashMaps in Java, preserving the order of inserted elements is crucial in certain scenarios. By default, HashMaps do not maintain the insertion order, resulting in a random ordering during iteration. To address this issue, you can utilize the LinkedHashMap class.

LinkedHashMap extends HashMap and offers the same functionality with an additional feature: it maintains the insertion order of the elements. This means that when you iterate over a LinkedHashMap, the elements are returned in the order they were initially inserted into the map.

To create a LinkedHashMap, simply instantiate it as follows:

<code class="java">import java.util.LinkedHashMap;

LinkedHashMap<String, String> linkedHashMap = new LinkedHashMap<>();</code>

Now, you can add elements to the LinkedHashMap as you would with a regular HashMap:

<code class="java">linkedHashMap.put("key1", "value1");
linkedHashMap.put("key2", "value2");</code>

However, when you iterate over the LinkedHashMap:

<code class="java">for (String key : linkedHashMap.keySet()) {
    System.out.println(key);
}</code>

The keys will be printed in the order they were inserted: "key1" followed by "key2".

Using LinkedHashMap ensures that the insertion order of elements is preserved, making it suitable for situations where maintaining the chronological sequence of data is essential.

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