Stringと数値の変換
7168 ワード
主にJDKのコードなのか、比較的クラシックなのか、見応えがあります.例えば:
package alg;
/**
* @author zha
*/
public class Alg3StringToint {
/**
* @param args
*/
public static void main(String[] args) {
String intv = "1232192373290";
// int value = Integer.parseInt(intv);
// System.out.println(value);
}
// JDK
public static int parseInt(String s, int radix)
throws NumberFormatException {
/*
* WARNING: This method may be invoked early during VM initialization
* before IntegerCache is initialized. Care must be taken to not use the
* valueOf method.
*/
if (s == null) {
throw new NumberFormatException("null");
}
if (radix < Character.MIN_RADIX) {
throw new NumberFormatException("radix " + radix
+ " less than Character.MIN_RADIX");
}
if (radix > Character.MAX_RADIX) {
throw new NumberFormatException("radix " + radix
+ " greater than Character.MAX_RADIX");
}
int result = 0;
boolean negative = false;
int i = 0, len = s.length();
int limit = -Integer.MAX_VALUE;
int multmin;
int digit;
if (len > 0) {
char firstChar = s.charAt(0);
if (firstChar < '0') { // Possible leading "+" or "-"
if (firstChar == '-') {
negative = true;
limit = Integer.MIN_VALUE;
} else if (firstChar != '+')
throw new NumberFormatException(s);
if (len == 1) // Cannot have lone "+" or "-"
throw new NumberFormatException(s);
i++;
}
multmin = limit / radix;
while (i < len) {
// Accumulating negatively avoids surprises near MAX_VALUE
digit = Character.digit(s.charAt(i++), radix);
if (digit < 0) {
throw new NumberFormatException(s);
}
if (result < multmin) {
throw new NumberFormatException(s);
}
result *= radix;
if (result < limit + digit) {
throw new NumberFormatException(s);
}
result -= digit;
}
} else {
throw new NumberFormatException(s);
}
return negative ? result : -result;
}
}