Question

I am using hashmap, but it is not working correctly. I have a class Computing.java, where I have method for adding into hashmap:

addIntoMap(String key, String value){

   m_parameters_values.put(key, value);
   }

and method for get from hashmap:

public void getValueByKey(String key){
        System.out.println("GET "+m_parameters_values.get(key));
    }

I am calling theese methods from Main class, but I am not able to be able to get keys, I am still getting null. Do you know why?

Content of class computing (constructors omitted):

public void Parse (String args[]) throws Exception{
        Parse(args,true);
    }

    public void Parse(String[] args, boolean throwErrorIfParamenterNotDefined) throws CmdLineException
    {


        int i = 0;

        while (i < args.length)
        {
            // The current string is a parameter name
            String key = args[i].substring(1, args[i].length() - 1).toLowerCase();
            String value = "";
            i++;
            if (i < args.length)
            {
                if (args[i].length() > 0 && args[i] == "-")
                {
                    // The next string is a new parameter, do not nothing
                } else
                {
                    // The next string is a value, read the value and move forward
                    value = args[i];
                    i++;
                }
            }

            if (!m_parameters.containsKey(key))
            {
                if (throwErrorIfParamenterNotDefined)
                {

                    //throw new CmdLineException("Parameter is not allowed.");

                }
                //continue;
            }
            System.out.println("Key: "+key+" value: "+value);
            m_parameters_values.put(key, value);
            //System.out.println("GET "+m_parameters_values.get("provider"));
            }

        // Check that required parameters are present in the command line. 

        for (String key : m_parameters.keySet())
        {
            if (m_parameters.get(key).required() && !m_parameters.get(key).exists())
                throw new CmdLineException("Required parameter is not found.");
        }


    }

    public void getValueByKey(String key){
        System.out.println("GET "+m_parameters_values.get(key));
    }

Content of main class:

public static void main(String[] args) {

    Computing comp = new Computing("Computing");    

        cmdLine.Parse(args);
        cmdLine.getValueByKey("convert");

Answer 1

print value used in put method.

Acc. to javadoc:

A return value of null does not necessarily indicate that the map contains no mapping for the key; it’s also possible that the map explicitly maps the key to null.

To be sure, use containsKey method to verify if key really exists.

use following code in getValueByKey; and see if it prints anything:

if (m_parameters.containsKey(key))
{
    System.out.println("GET "+m_parameters_values.get(key));
}