java 判断一个字符串是否为数字

public class num1 {
public static boolean isNum(String str){
return str.matches("^[-+]?(([0-9]+)([.]([0-9]+))?|([.]([0-9]+))?)$");
}
public static void main(String[] args) {
String str1="0123";
String str2="12-3";
String str3="1.2";
String str4="1.2.3";
String str5="12*3";
String str6="a123";
System.out.println(str1+":"+isNum(str1));
System.out.println(str2+":"+isNum(str2));
System.out.println(str3+":"+isNum(str3));
System.out.println(str4+":"+isNum(str4));
System.out.println(str5+":"+isNum(str5));
System.out.println(str6+":"+isNum(str6));
}
}