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javanumberformatexceptionparseint

In Java, why does `Integer.parseInt("10000000000000000000000000000000"), 2)` throw a NumberFormatException?

I'm using OpenJDK17 and am perplexed as to why Integer.parseInt("10000000000000000000000000000000", 2) would throw a NumberFormatException as it is the binary representation of Integer.MIN_VALUE (or -2147483648 in decimal).

Is this expected or some known edge-case/quirk?

I attempted to provide the binary representation of Java's Integer.MIN_VALUE to Integer.parseInt in order to receive back -2147483648 but inside experience a NumberFormatException.

Note: I'm not particularly trying to achieve anything just fiddling around on the JVM and came across this.

Solution

  • The Integer.parseInt() method with the radix of 2 is not used to convert a bit representation of a two's complement integer value to an int value. Instead it "just" parsed the string as a signed integer with the given radix. What that means is that "10000000000000000000000000000000" in binary is 2147483648 in decimal. Such a big value cannot be saved as int in java because the maximum int value in java is 2147483647 (or Integer.MAX_VALUE). That's why you get a NumberFormatException. The result will not be a negative value like Integer.MIN_VALUE what you expected. The result will only be negative when the first character in the string is a - character as mentioned in the javadoc of Integer.parseInt():

    [...] except that the first character may be an ASCII minus sign '-' ('\u002D') to indicate a negative value [...]