可以将常量值传递给功能参数吗？

Question

I'm a computer science student, and I was studying homework earlier last night. I stumbled upon a function in my book that I thought was redundant, but upon further inspection I have gotten rather "confused"

public int refundBalance() {
  int amountToRefund = balance;
  balance = 0;
  return amountToRefund;
}

As I looked at this, I thought that having to create a new local variable to store and pass data around was rather redundant, so I thought up this:

refundBalance(balance);
public int refundBalance(int amount) {
  balance = 0;
  return amount;
}

But obviously, i'm just "trading lines".

Question: Is there any way to always pass the same parameter to a function, without having to pass the value on call?

Optional Question : How would/could you optimize this function? (If even possible)

Thanks all <3 (PS this is not a homework assignment, it's just basic curiosity.)

Answer 1

In reality, you actually probably want to access the balance atomically and protect it from multiple threads having access. If that's the case, you can use an AtomicInteger to do this in one shot via getAndSet .

import java.util.concurrent.atomic.AtomicInteger;

private final AtomicInteger balance = new AtomicInteger();

public int refundBalance() {
  return balance.getAndSet(0);
}

This is actually what I'd recommend on top of using synchronized on the method and writing it as you have above. It also happens to be one line :-).

Answer 2

The original code is a fine, standard object oriented practice.

There is a state, a private field balance , which you can only modify by public methods, ensuring that accountancy is safe.

Now for doing the function without local variable:

public int refundBalance() {
    try {
        return balance;
    } finally {
        balance = 0;
    }
}

This should do:

• push value of balance
• store 0 into balance
• return

Answer 3

If you mean via a default parameter, then no. Since refundBalance is a public method and the class that encloses it stores the balance variable, it wouldn't make sense for an outside object to be able to determine the amount to refund - you could provide a refundAmount method with an amount parameter if you wanted that functionality.

As for the optional question, I think that trying to optimize that function is pointless - it's fine as it is and you wouldn't gain any performance increase.