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copied!<p><a href="https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2" rel="noreferrer"><code>Dictionary</code></a> is probably the closest. <code>System.Collections.Generic.Dictionary</code> implements the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.idictionary-2" rel="noreferrer"><code>System.Collections.Generic.IDictionary</code></a> interface (which is similar to Java's <code>Map</code> interface).</p> <p>Some notable differences that you should be aware of:</p> <ul> <li>Adding/Getting items <ul> <li>Java's HashMap has the <code>put</code> and <code>get</code> methods for setting/getting items <ul> <li><code>myMap.put(key, value)</code></li> <li><code>MyObject value = myMap.get(key)</code></li> </ul></li> <li>C#'s Dictionary uses <code>[]</code> indexing for setting/getting items <ul> <li><code>myDictionary[key] = value</code></li> <li><code>MyObject value = myDictionary[key]</code></li> </ul></li> </ul></li> <li><code>null</code> keys <ul> <li>Java's <code>HashMap</code> allows null keys</li> <li>.NET's <code>Dictionary</code> throws an <code>ArgumentNullException</code> if you try to add a null key</li> </ul></li> <li>Adding a duplicate key <ul> <li>Java's <code>HashMap</code> will replace the existing value with the new one.</li> <li>.NET's <code>Dictionary</code> will replace the existing value with the new one if you use <code>[]</code> indexing. If you use the <code>Add</code> method, it will instead throw an <code>ArgumentException</code>.</li> </ul></li> <li>Attempting to get a non-existent key <ul> <li>Java's <code>HashMap</code> will return null.</li> <li>.NET's <code>Dictionary</code> will throw a <code>KeyNotFoundException</code>. You can use the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.trygetvalue" rel="noreferrer"><code>TryGetValue</code></a> method instead of the <code>[]</code> indexing to avoid this:<br> <code>MyObject value = null; if (!myDictionary.TryGetValue(key, value)) { /* key doesn't exist */ }</code></li> </ul></li> </ul> <p><code>Dictionary</code>'s has a <a href="https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.containskey" rel="noreferrer"><code>ContainsKey</code></a> method that can help deal with the previous two problems.</p>

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