[java] Converting characters to integers in Java

Can someone please explain to me what is going on here:

char c = '+';
int i = (int)c;
System.out.println("i: " + i + " ch: " + Character.getNumericValue(c));

This prints i: 43 ch:-1. Does that mean I have to rely on primitive conversions to convert char to int? So how can I convert a Character to Integer?

Edit: Yes I know Character.getNumericValue returns -1 if it is not a numeric value and that makes sense to me. The question is: why does doing primitive conversions return 43?

Edit2: 43 is the ASCII for +, but I would expect the cast to not succeed just like getNumericValue did not succeed. Otherwise that means there are two semantic equivalent ways to perform the same operation but with different results?

This question is related to java integer type-conversion character primitive

The answer is


Try any one of the below. These should work:

int a = Character.getNumericValue('3');
int a = Integer.parseInt(String.valueOf('3');

As the documentation clearly states, Character.getNumericValue() returns the character's value as a digit.
It returns -1 if the character is not a digit.

If you want to get the numeric Unicode code point of a boxed Character object, you'll need to unbox it first:

int value = (int)c.charValue();

43 is the dec ascii number for the "+" symbol. That explains why you get a 43 back. http://en.wikipedia.org/wiki/ASCII


Character.getNumericValue(c)

The java.lang.Character.getNumericValue(char ch) returns the int value that the specified Unicode character represents. For example, the character '\u216C' (the roman numeral fifty) will return an int with a value of 50.

The letters A-Z in their uppercase ('\u0041' through '\u005A'), lowercase ('\u0061' through '\u007A'), and full width variant ('\uFF21' through '\uFF3A' and '\uFF41' through '\uFF5A') forms have numeric values from 10 through 35. This is independent of the Unicode specification, which does not assign numeric values to these char values.

This method returns the numeric value of the character, as a nonnegative int value;

-2 if the character has a numeric value that is not a nonnegative integer;

-1 if the character has no numeric value.

And here is the link.


public class IntergerParser {

public static void main(String[] args){
String number = "+123123";
System.out.println(parseInt(number));
}

private static int parseInt(String number){
    char[] numChar = number.toCharArray();
    int intValue = 0;
    int decimal = 1;
    for(int index = numChar.length ; index > 0 ; index --){
        if(index == 1 ){
            if(numChar[index - 1] == '-'){
                return intValue * -1;
            } else if(numChar[index - 1] == '+'){
                return intValue;
            }
        }
        intValue = intValue + (((int)numChar[index-1] - 48) * (decimal));
        System.out.println((int)numChar[index-1] - 48+ " " + (decimal));
        decimal = decimal * 10;
    }
    return intValue;
}

From the Javadoc for Character#getNumericValue:

If the character does not have a numeric value, then -1 is returned. If the character has a numeric value that cannot be represented as a nonnegative integer (for example, a fractional value), then -2 is returned.

The character + does not have a numeric value, so you're getting -1.

Update:

The reason that primitive conversion is giving you 43 is that the the character '+' is encoded as the integer 43.


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