如何比较一个整数和一个长？

Question

I am trying to check if a long integer is greater than the INTEGER.MAX value but it's not working. It's very straight forward so I am just wondering if there is some problem with comparing an Integer object with a long as I have done because otherwise I don't know what the problem is. At the moment when the nextTotal value exceeds INTEGER.MAX, it kicks into negative numbers instead of printing the error message.

public Integer initialValue=0;

int amount = Integer.parseInt(amountStr);
        System.out.println("Received from client: " + amount);

        long nextTotal=amount+initialValue;
            if((nextTotal>Integer.MAX_VALUE)||    (nextTotal<Integer.MIN_VALUE)){
                System.out.println("Error: Integer has not been added as the total exceeds the Maximum Integer value!");
                out.flush();
            }  

            else{
                initialValue+=amount;
                out.println(initialValue); //server response
                System.out.println("Sending total sum of integers to the client:"+initialValue);
                out.flush();
                }
            }

Answer 1

The problem is that you have added two int s, but they haven't been promoted to long yet, so it overflows before being converted to a long , and of course an int can never be greater than Integer.MAX_VALUE . It will only get converted to a long upon assignment, which is after the addition.

Convert to a long before the addition, with a cast.

long nextTotal = (long) amount + initialValue;

Answer 2

Since you don't really want to use a long value, I would normally do the check like this:

int amount = Integer.parseInt(amountStr);
if (amount > (Integer.MAX_VALUE - initialValue)) 
  throw new IllegalArgumentException("Amount exceeds maximum value");
initialValue += amount;

In other words, check whether the amount will overflow before adding, and throw an exception (or send an error message or whatever is appropriate for your application) instead of proceeding normally.