String to Integer (atoi)

class Solution {
public int myAtoi(String str) {

       if (str == null) {
            return 0;
        }

        str = str.trim();
        if ("".equals(str)) {

            return 0;
        }

        if (str.contains(".")){
            int index = str.indexOf('.');
            if (index == 0) {
                return 0;
            }else {
                str = str.substring(0,index);
            }
        }
        System.out.println(str);
        StringBuilder stringBuilder = new StringBuilder();
        char[] chars = str.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            if ("-".equals(chars[i]+"") || "+".equals(chars[i]+"")) {
                if (stringBuilder.toString().contains("-") || stringBuilder.toString().contains("+")) {
                     break;
                }
                stringBuilder.append(chars[i]);
            }else if (Character.isDigit(chars[i])) {
                if ("0".equals(chars[i])) {
                    continue;
                }else {
                    stringBuilder.append(chars[i]);
                }
            }else {
                break;
            }
        }
        if (stringBuilder.length() == 0 ||
                (stringBuilder.length() == 1 && "-".equals(stringBuilder.toString())) ||
                (stringBuilder.length() == 1 && "+".equals(stringBuilder.toString()))
                ) {
            return 0;
        }

        double bigDecimal = Double.valueOf(stringBuilder.toString());

        if (bigDecimal > Integer.MAX_VALUE || bigDecimal < Integer.MIN_VALUE) {
            return 0;
        }
        return Integer.valueOf(stringBuilder.toString());
}

}