Java retrieve value from TreeMap<String, TreeMap<String, Integer>>

Question

I'm pretty new to Maps and I'm quite stuck. I have the following TreeMap:

TreeMap<String, Map<String, Integer>> routes = new TreeMap<String, Map<String, Integer>>();

Let's say, for example, my TreeMap is filled as follows:

{A={B=10, C=15, D=20}, B={C=35, D=25}, D={C=30}}

Now I'm trying to print out the Integer value from my TreeMap and assign it to an int x = routes.get(0).get(0) but I'm getting the following error:

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer

After a bit of reading, I understood that I'm trying to cast an String object into an Integer object which is not correct and that’s why Java throws the error meaning my x is being assigned to B and not 10.

So my question is how do I assign x to the value of 10?

I find this strange. Normally .get would return null if the key didn't exist (or happened to map to null), and you'd get a NullPointerException instead. — Makoto
– Makoto, Commented May 16, 2015 at 15:48

Makoto · Accepted Answer · 2015-05-16 15:46:39Z

2

.get() is attempting to use the key of the map that you've declared. Since you want to find the value within Map[A][B], then you should refer to it as such:

int x = routes.get("A").get("B");

answered May 16, 2015 at 15:46

Makoto

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6 Comments

nTuply Over a year ago

I'm using it in a loop so I can make an adjacency matrix based on those values. So I cannot use "A" or "B" but have to use i or j which are integers(from my nested for loops)

Makoto Over a year ago

I think your design's wrong, then. You're mapping String to String to int; you have no other way to get through the mapping with anything other than Strings.

nTuply Over a year ago

What would be a better way to make it?

Makoto Over a year ago

That's a broader question than what you've phrased here, I'm afraid. Although, if you're looking for hints on adjacency matrices, then you should search this site. There are a lot of approaches to it in Java.

nTuply Over a year ago

I edited the question a bit, but thanks anyways. I'll look into it.

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