Repleting a value to its original value after depletion

Question

In my class I have:
public int charge;This holds a value which set by me in the constructor when I instantiate the class in main(). This value represents a battery, and the value I give it at the start of my test represents a full battery. As the code runs, the value of charge is depleted incrementally (charge--). When charge equals 0, it requests the Charger class to "recharge" the battery and restore the charge to its value, which I assigned to it at the beginning.
In my test, I will instantiate the class with the charge several different times, and I will assign each object's charge a different value since all batteries are not made equal and some last longer than others. However, what I am stuck with is figuring out how to use the recharge() method I have in my Charger class to completely restore the battery instantly (and not incrementally as it was depleted). Any ideas on what the recharge() method should look like?

Answer 1

In your code you have:
Charger charger;Later on you try to use charger. This should give you a null reference error, not a syntax error. If you have charger created someplace else, that statement overrides its declaration in the external scope and creates a local variable to hold a reference. You do not initialize that variable with any reference to an external object, nor create one in the scope.
My way of thinking you need 3 classes:
1 - Battery
2 - Charger
3 - Device (to use the Battery or consume the charge).
The Battery will need to be used by the other 2 classes, as such, you need to be able to pass a reference of Battery to those. To do that you need your methods to accept a reference to Battery. This will make your Charger and Device classes able to work on all of your Battery objects.
public void recharge(Battery b){
  b.currentCharge = b.maxCharge;
public void useEnergy(Battery b){
  b.currentCharge -= 3; //some drain amount, I arbitrarily chose 3.
  if(b.currentCharge<0) b.currentCharge = 0;
}