CODEWITHSUNDEEP
java
Dany77
Dany77

Reputation: 21

nullPointerException with enums

I'm coding a game where the player has to type something in the dialog field, and java has to interpret it as an action. I have a class named GameEngine where i use a switch :

public void interpretCommand(final String commandLine) 
{
    Command command = parser.getCommand(commandLine);
    CommandWord commandWord = command.getCommandWord();
    switch ( commandWord ) {
      case UNKNOWN: 
         gui.println("Unknown command...");
         return;
      case LOAD: 
         load(); 
         break;
    } 
}

Enums used here are in an enumclass :

public enum CommandWord
{
    LOAD("charger"),UNKNOWN("?");
    private String commandWord;
 }

and finally, the CommandWords class :

public class CommandWords
{
    // a HashMap that holds all valid command words
   private HashMap<String, CommandWord> validCommands; 

   public CommandWords()
   {
      validCommands = new HashMap<String, CommandWord>();
      for(CommandWord command : CommandWord.values()) {
          if(command != CommandWord.UNKNOWN){
              validCommands.put(command.toString(), command);
          }
      }
   }


   /**
     * @param commandWord the command word to look for in the valid commands
     * @return the commandWord associated with the word typed
     */
    public CommandWord getCommandWord(final String commandWord)
    {
        CommandWord command =validCommands.get(commandWord);
        if(command !=null) {
           return command;
        }
        else {
           return CommandWord.UNKNOWN;
        }
    }

the Command class :

public class Command
{
    private CommandWord commandWord;

    /**
     * @param commandWord from enum class
     */
    public Command(CommandWord commandWord)
    {
        this.commandWord = commandWord;
    }

    public CommandWord getCommandWord()
    {
        return commandWord;
    }
}

My problem is very simple: when I type charger, it works, but when I type a random word, not in the list, I get a NullPointerException in terminal at the line 

        switch ( commandWord )

in interpretCommand.

I can't see what's wrong with my code. If someone could help, thank you. Please don't blame me, I'm a novice, I just started a few months ago!

Solution : in command modify/add these lines

    public boolean isUnknown()
{
    return (commandWord == null);
}

    public CommandWord getCommandWord()
{
    if(!isUnknown()){

    return commandWord;

}
 else return CommandWord.UNKNOWN;
}

Upvotes: 0

Views: 4185

Answers (1)

Henry
Henry

Reputation: 43798

There is only one thing that can be null at this line and that is commandWord. So your method call command.getCommandWord() returns null.

EDIT: With the information you have provided now, this means that the parser gives back a Command object which has no commandWord set.

Upvotes: 2

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