returning doubles with 2 decimals JAVA

Hi all. I'm writing a program where users input the cost of an item (in the constructor), so for example,

Item (string name, double cost, int qty) { ... }

I have a method

public double getCost() {
...
}

And I want it to return the cost. I tried using DecimalFormat, but I was told that it doesn't change the number itself. I need to return a Double, not a String!!

So when my client queries:

item.getCost()

They are give a double in return, example,

3.00

I tried this, but it didn't work:

DecimalFormat df = new DecimalFormat("#0.00");
String itemCost = (df.format(cost));
cost = Double.parseDouble(itemCost);
return cost;
}

It needs to return a string but I need it to return a double. Help please.