8.String_to_Integer.java

public class Solution {
	private static final int maxDiv10 = Integer.MAX_VALUE / 10;
    public int myAtoi(String str) {
    	int i = 0, n = str.length();
		while (i < n && Character.isWhitespace(str.charAt(i)))
			i++;
		int sign = 1;
		if (i < n && str.charAt(i) == '+')
			i++;
		else if (i < n && str.charAt(i) == '-') {
			sign = -1;
			i++;
		}
		int num = 0;
		while (i < n && Character.isDigit(str.charAt(i))) {
			int digit = Character.getNumericValue(str.charAt(i));
			if (num > maxDiv10 || num == maxDiv10 && digit >= 8)
				return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
			num = num * 10 + digit;
			i++;
		}
		return sign * num;    
    }
}