《Java知識應用》Java 判斷字符串是否爲數字

正則表達式：(-|\\+)?([1-9]\\d*\\.?\\d*)|(0\\.\\d*[0-9]) 

案例：

public class NumberUtil {

    /**
     * 判斷是否爲數字
     * @param str
     * @return
     */
    public static boolean isDecimal(String str) {
        if (str == null || Objects.equals(str,"")) {
            return false;
        } else {
            String REGEX = "(-|\\+)?([1-9]\\d*\\.?\\d*)|(0\\.\\d*[0-9])";
            Pattern p = Pattern.compile(REGEX);
            Matcher m = p.matcher(str);
            return m.matches();
        }
    }

    public static void main(String[] args) {
        System.out.println(isDecimal("0.0"));
        System.out.println(isDecimal("1.0"));
        System.out.println(isDecimal("-1.0"));
        System.out.println(isDecimal("+1000000.0"));
        System.out.println(isDecimal("+1000000"));
        System.out.println(isDecimal("-1000000"));
        System.out.println(isDecimal(""));
        System.out.println(isDecimal("127.0.0.1"));
        System.out.println(isDecimal(".127"));
        System.out.println(isDecimal("s.127"));
    }
}

運行結果：