I'm fairly new to java, but I'm sure I've done this before and now it's not working right. What am I forgetting here?

LeftPanel class

Inventory inventory;
JTextField txtMoney = new JFormattedTextField(inventory.getInvWallet());

Inventory class

public class Inventory {

	public int invId = 0;
	public int invPrice = 0;
	public String invName = "";
	public double invWallet=100;
	
	public Inventory(int invId, int invPrice, String invName, double invWallet){
		this.invId = invId;
		this.invPrice = invPrice;
		this.invName = invName;
		this.invWallet = invWallet;
	}
	
	public double getInvWallet(){
		return invWallet;
	}
	public void setInvWallet(double invWallet){
		this.invWallet = invWallet;
	}
	
}

The error I get

Exception in thread "main" java.lang.NullPointerException
	at LeftPanel.<init>(LeftPanel.java:14)
	at Sim.main(Sim.java:17)

Thanks muchly to those who answer

You need to initialize the object with the keyword new, like

Object o = new Object();

Or in your case you need to initialize the Inventory object. All declared and not explicitly initialized objects are initialized to null, hence the NullPointerException

You have declared the object for the Inventory class. But you have not allocated the memory for it. So you have to write that statement explicitly.

Inventory inventory;
inventory = new Inventory();
JTextField txtMoney = new JFormattedTextField(inventory.getInvWallet());

Hope this will work fine for you. Try it out and please do let me know.

Thank you both, that seemed to be the problem. I usually put that but I forgot on this one :P
I have another issue now, though.

Part of my program needs to read through the list of employees I have in the employee class (similar to the inventory class) and check whether they've been hired already or not, but I'm not entirely sure how to do that. I can do

employee.getEmployeeId()

but how do I get the next Id and the next, next, next, etc.?

I'm thinking I'll have to reorganize the entire program and store the list in arrays and a .txt or something. Is this a bad idea, or are there reasons why I shouldn't do this method instead?