Check if Integer is too great

Question

I am working on an exchange system and the user is setting the price and amount for an exchange.

I want to make sure that the exchange is no greater than the Integer maximum value, but I am running into a problem.

When the amount of the exchange is put to 9 or more, even though I have a check to make sure the number is no greater than the maximum value, it does not work. I have done some debugging and when setting the amount to 9 while the price is 2,147,483,646 (1 less than the max number), it prints out this:

2,147,483,630 - 9

This is my debugging code, what should I add to it to make sure that this does not happen?

public void setPrimaryAmount(int primaryAmount) {
        int price = primaryAmount * this.price;
        System.out.println(Misc.format(this.price * primaryAmount) + " - " + primaryAmount);
        if (price > Integer.MAX_VALUE ||
                price == Integer.MAX_VALUE ||
                price >= Integer.MAX_VALUE ||
                price < 0 || price <= 0 ||
                price++ == Integer.MAX_VALUE) {
            System.out.println("Attempted to set a bad amount.");
            return;
        }
        this.primaryAmount = primaryAmount;
    }

"Attempted to set a bad amount" prints out until you enter an amount >= 9.

Solution 1

You can't store a value in an int, and then check to see whether it's too big for an int. Store it in a long instead.

long price = (long)primaryAmount * (long)this.price;

Solution 2

In Java 8, one approach would be to use

Math.addExact(int, int);

which according to Javadocs will throw an ArithmeticException if the result overflows an int. In other versions, I would recommend what Flight Odyssey suggested and use longs at least for these types of checks.

Comments

[Ted Hopp]

You do realize, I hope, that tests like price < 0 || price <= 0 are redundant: price <= 0 is entirely sufficient. Likewise for price > Integer.MAX_VALUE || price == Integer.MAX_VALUE || price >= Integer.MAX_VALUE, except there's the added wrinkle that an integer variable can never be greater than Integer.MAX_VALUE so price == Integer.MAX_VALUE is all you need.

[Radiodef]

Note that switching to longs for good ensures you can sell a planet without overflow.

[Lee Fogg]

@Tyluur We accept as answer (select the tick) when we're happy an answer resolves our concern.