34 lines
1.2 KiB
Java
34 lines
1.2 KiB
Java
|
package Maths;
|
||
|
|
|
||
|
|
public class ParseInteger {
|
||
|
|
public static void main(String[] args) {
|
||
|
|
assert parseInt("123") == Integer.parseInt("123");
|
||
|
|
assert parseInt("-123") == Integer.parseInt("-123");
|
||
|
|
assert parseInt("0123") == Integer.parseInt("0123");
|
||
|
|
assert parseInt("+123") == Integer.parseInt("+123");
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Parse a string to integer
|
||
|
|
*
|
||
|
|
* @param s the string
|
||
|
|
* @return the integer value represented by the argument in decimal.
|
||
|
|
* @throws NumberFormatException if the {@code string} does not contain a parsable integer.
|
||
|
|
*/
|
||
|
|
public static int parseInt(String s) {
|
||
|
|
if (s == null) {
|
||
|
|
throw new NumberFormatException("null");
|
||
|
|
}
|
||
|
|
boolean isNegative = s.charAt(0) == '-';
|
||
|
|
boolean isPositive = s.charAt(0) == '+';
|
||
|
|
int number = 0;
|
||
|
|
for (int i = isNegative ? 1 : isPositive ? 1 : 0, length = s.length(); i < length; ++i) {
|
||
|
|
if (!Character.isDigit(s.charAt(i))) {
|
||
|
|
throw new NumberFormatException("s=" + s);
|
||
|
|
}
|
||
|
|
number = number * 10 + s.charAt(i) - '0';
|
||
|
|
}
|
||
|
|
return isNegative ? -number : number;
|
||
|
|
}
|
||
|
|
}
|