Here you can find the source of isDouble(String str)
public static boolean isDouble(String str)
//package com.java2s; import java.util.regex.Pattern; public class Main { public static boolean isDouble(String str) { Pattern pattern = Pattern.compile("^[-\\+]?[.\\d]*$"); return pattern.matcher(str).matches(); }/*from ww w . j a v a2s.c om*/ }