How to Map Multiple Values to a Single Key in a Java HashMap?

Mapping Multiple Values to a Single Key in HashMap

In Java's HashMap, each key is associated with a single value. However, there are scenarios where you may need to map multiple values to a single key. Here's how you can achieve this:

The MultiValueMap Approach:

The simplest and most straightforward approach is to use a Map of List. This involves creating a HashMap where the values are ArrayLists containing multiple values. For instance:

<code class="java">Map<Object, ArrayList<Object>> multiMap = new HashMap<>();</code>

To add multiple values for a specific key, you can use the put() method:

<code class="java">multiMap.put("key", new ArrayList<Object>() {{
    add("value1");
    add("value2");
    add("value3");
}});</code>

To retrieve the values, you can use the get() method to obtain the ArrayList and then iterate over it:

<code class="java">List<Object> values = multiMap.get("key");
for (Object value : values) {
    // Do something with the value
}</code>

In this example, values will contain a List with ["value1", "value2", "value3"]. You can then access the desired value based on its index (i.e., values.get(2) for the third value).

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