NullPointerException while using put method of HashMap
-
09-09-2019 - |
Question
The following code is giving me a NullPointerException
. The problem is on the following line:
...
dataMap.put(nextLine[0], nextLine[6]);
What is strange is that I have run this code without the above line and the call to nextLine[0]
and nextLine[6]
work exactly as expected - that is they give me back elements of a csv file. I declare and initialise the HashMap
with the code
HashMap<String, String> dataMap = null;
earlier in the method
String[] nextLine;
int counter=0;
while (counter<40) {
counter++;
System.out.println(counter);
nextLine = reader.readNext();
// nextLine[] is an array of values from the line
System.out.println(nextLine[0] + " - " + nextLine[6] +" - " + "etc...");
dataMap.put(nextLine[0], nextLine[6]);
}
return dataMap;
}
Solution
HashMap<String, String> dataMap = new HashMap<String,String>();
Your dataMap
variable isn't initialized at this point. You should be getting a compiler warning about that.
OTHER TIPS
Where is datamap initialised ? It's always null.
To clarify, you declare the variable and set it to null. But you need to instantiate a new Map, whether it's a HashMap or similar.
e.g.
datamap = new HashMap();
(leaving aside generics etc.)
dataMap is declared but not initialized. It can be initialized with
datamap = new HashMap();
Well, there are three objects accessed on that line. If nextLine[0] and nextLine[6] aren't null, because the println call above worked, then that leaves dataMap. Did you do dataMap = new HashMap(); somwehere?
Um, what exactly do you expect when you do this?
HashMap<String, String> dataMap = null;
...
dataMap.put(...)