Create Multidimensional HashMap in java

java arraylist hashmap xmlnode
Pablo picture Pablo · Feb 27, 2014 · Viewed 7.7k times · Source

I am kind of new to java, I have this code

...
NodeList indexEntryList = sourceDoc.getElementsByTagName("in.ar");  //this is a xml tag
for (int i = 0; i < indexEntryList.getLength(); i++) {
    ...
}
...

I have to create a HashMap (or something like this), where I save a String which is an attribute of the node, and a List of all nodes that have the same attribute.

I think something like this:

Map<String, ArrayList<Node>> indexCategories = new HashMap<String, ArrayList<Node>>();

But in each time of the for, I dont know how to search in all keys of the Map, and add the new Node to the list, and if the key does no exists yet, create the new item inside the Map.

Answer

Smutje picture Smutje · Feb 27, 2014

Use Map#containsKey() for searching if a key is present, Map#get() for obtaining the collection (if present) respective Map#put() for storing the newly created map. Everything could be found properly documented in the Map API, by the way.

Related questions

When to use HashMap over LinkedList or ArrayList and vice-versa

What is the reason why we cannot always use a HashMap, even though it is much more efficient than ArrayList or LinkedList in add,remove operations, also irrespective of the number of the elements. I googled it and found some …

Read More
why HashMap Values are not cast in List?

I'm putting values into the hashmap which is of the form, Map<Long, Double> highLowValueMap=new HashMap<Long, Double>(); highLowValueMap.put(1l, 10.0); highLowValueMap.put(2l, 20.0); I want to create a list by using values() method of …

Read More
Which Java Collection should I use?

In this question How can I efficiently select a Standard Library container in C++11? is a handy flow chart to use when choosing C++ collections. I thought that this was a useful resource for people who are not sure which …

Read More