方式一 :
  String str = "12354";
  System.out.println("str = " + str);
  System.out.println("判斷str是否為數字  = " + str.matches("[0-9]+"));

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方式二 :
String   a   =  "12345";
Pattern   regex   =   Pattern.compile( "[0-9]* ");
Matcher   match   =   regex.matcher(a);
boolean   flag   =   match.matches();