What is difference between null and empty list?

Question

List> pcList = null;
Map pcMap = new HashMap();
ComputerConfigurations tempPC = null;

if         


        

Answer 1

You're not initialising pcList at any point. Try this:

    final List> pcList = new LinkedList<>();
    Map pcMap = new HashMap();
    ComputerConfigurations tempPC = null;

    if (historyList != null) {
        Iterator iterator = historyList.iterator();
        while (iterator.hasNext()) {
            tempPC = (ComputerConfigurations) iterator.next();
            pcMap.put(tempPC.getEnvironment(), tempPC);
            pcList.add((Map) pcMap);
        }
    }