Determine whether a character is a number in Java

一、使用自带函数isDigit()

语法：

public static boolean isDigit(char ch)

实例：

public static boolean isNumeric (String str) {
    for (int i = str.length(); --i >=0) {
          if (!Character.isDigit(str.charAt(i))) {
                return false;
          }
    }
    return true;}

二、使用正则表达式

实例1：

public static boolean isNumeric(String str) {
    Pattern pattern = Pattern.compile("^[-\\+]?[\\d]*$");
    return pattern.matcher(str).matches();}

实例2：

public static boolean isNumeric(String str) {
    if (str != null && !"".equals(str.trim())) {
          return s.matches("^[0-9]*$");
    }
    return false;}

实例3：

 public static boolean isNumeric (String str) {
    Pattern pattern = Pattern.compile("[0-9]*");
    return pattern.matcher(str).matcher();}

三、使用ASCII码

public static boolean isNumeric (String str) {
    for (int i = str.length(); --i>=0;) {
        int chr = str.charAt(i);
        if (chr < 48 || chr > 57) {
            return false;
        }
   }
   return true;}

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