Question

So I had a question on here the other day about how to accessing the same data class with two different other classes without creating separate instances. It was recommended to use a singleton so i have done some research but there isn’t a lot about it.

The issue I’m having is that my main class gets a null pointer exception when trying to access the data singleton. But my other class can access it and get the data just fine. How exactly is that possible? I have a pretty basic setup…

singleton

public enum laneData {
    INSTANCE;
    private String laneID;

    public String getLaneID() {
        return laneID;
    }

    public void setLaneID(String laneID) {
        this.laneID = laneID;
    }

}

main class call

 private laneData laneData;
 public void init() {
     laneData.setLaneID("test"); //these two lines each throw null pointer unless commented out
     System.out.println(laneData.getLaneID()); 
     ....

other class

public class XMLParser {
private LaneGUI laneGUI;
private laneData laneData;


public void parseInputString(String input){ 
laneData.setLaneID(getCharacterDataFromElement(line));  //both of these work fine
System.out.println("stored ID: " + laneData.getLaneID());

Answer 1

You need private laneData laneData = laneData.INSTANCE;.

You can also just use laneData.INSTANCE.getLaneID().

Java guidelines also recommend than Class and Enum names be capitalized, I.E. LaneData.