Parsing a Hexadecimal String to an Integer throws a NumberFormatException?

So, In Java, you know how you can declare integers like this:

int hex = 0x00ff00;

I thought that you should be able to reverse that process. I have this code:

Integer.valueOf(primary.getFullHex());

where primary is an object of a custom Color class. It's constructor takes an Integer for opacity (0-99) and a hex String (e.g. 00ff00).

This is the getFullHex method:

public String getFullHex() {
    return ("0x" + hex);
}

When I call this method it gives my this NumberFormatException:

java.lang.NumberFormatException: For input string: "0xff0000"

I can't understand what's going on. Can someone please explain?

Will this help?

Integer.parseInt("00ff00", 16)

16 means that you should interpret the string as 16-based (hexadecimal). By using 2 you can parse binary number, 8 stands for octal. 10 is default and parses decimal numbers.

In your case Integer.parseInt(primary.getFullHex(), 16) won't work due to 0x prefix prepended by getFullHex() - get rid of and you'll be fine.

Integer.valueOf(string) assumes a decimal representation. You have to specify that the number is in hex format, e.g.

int value = Integer.valueOf("00ff0000", 16); 

Note that Integer.valueOf(string,16); does not accept a prefix of 0x. If your string contains the 0x prefix, you can use Integer.decode("0x00ff0000");

Try to use decode method:

Integer.decode("0x00ff00");

DecodableString:

• Signopt DecimalNumeral
• Signopt 0x HexDigits
• Signopt 0X HexDigits
• Signopt # HexDigits
• Signopt 0 OctalDigits

You can read about it here https://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#decode(java.lang.String)

The parseInt method only accepts the number part, not any kind of "base" indicator such as "0x" for hexadecimal or "0" for octal. Use it like this

int decimal = Integer.parseInt("1234", 10);
int octal = Integer.parseInt("1234", 8);
int hex = Integer.parseInt("1234", 16);

This should do it:

String hex = "FA"; 
int intValue = Integer.parseInt(hex, 16);

And if you want to generate hex representation of an integer, use

String hex = Integer.toHexString(12);