How to put an array object in hashmap?
<p>I'm trying to solve this but I'm stuck here for a while now. My problem is I can't find a way on how to put an array object to my hashmap. </p>

<p>Here's my example code of hashmap for dropdown menu that I got from google.</p>

<pre><code>private Map&lt;String,Map&lt;String,String&gt;&gt; data2 = new HashMap&lt;String,Map&lt;String,String&gt;&gt;();
private String country; 
private String city;  
private Map&lt;String, String&gt; countries;
private Map&lt;String,String&gt; cities;

 countries  = new HashMap&lt;String, String&gt;();
        countries.put("USA", "USA");
        countries.put("Germany", "Germany");
        countries.put("Brazil", "Brazil");

        Map&lt;String,String&gt; map = new HashMap&lt;String, String&gt;();
        map.put("New York", "New York");
        map.put("San Francisco", "San Francisco");
        map.put("Denver", "Denver");
        data2.put("USA", map);

        map = new HashMap&lt;String, String&gt;();
        map.put("Berlin", "Berlin");
        map.put("Munich", "Munich");
        map.put("Frankfurt", "Frankfurt");
        data2.put("Germany", map);
</code></pre>

<p>Now.. My problem is how to put my objects into hashmap. </p>

<p>Here's my code in fetching the array object.</p>

<pre><code>     while(rs.next()){
                     PropertyData reader = new PropertyData();
                     id = rs.getInt("id");
                     prop_name = rs.getString("prop_name");
                     prop_value = rs.getString("prop_value");
                     engine_name = rs.getString("engine_name");
                     //other setter..


                     reader.setId(id);
                     reader.setPropName(prop_name);
                     reader.setPropValue(prop_value);
                     reader.setEngineName(engine_name);
                     //other setter..

                     prop.add(reader);
                 }
</code></pre>

<p>From the code above. I want to put the <strong>id</strong> on hashmap key and <strong>propname</strong> on hashmap string name. Once selected, I want to display other values referencing the <strong>id</strong>. </p>

<p>And this is where my object has been added. </p>

<pre><code>    static List&lt;PropertyData&gt; prop = new ArrayList&lt;PropertyData&gt;();
</code></pre>

<p>I tried to initialized it on my hashmap but it returned null.</p>