Java第二次上机（正则表达式）

编写一个程序，判断一个字符串是否是合法的Java标识符；

//create string 
import java.util.regex.*;
public class Split {
    public static void main (String[] args) {
        Pattern pattern = Pattern.compile("[,]");
        String[] arrStr = pattern.split("abstract,break,byte,boolean,catch,case,class,char,continue,default,double,do,else,extends,false,final,float,for,finally,if,import,implements,int,interface,instanceof,long,length,native,new,null,package,private,protected,public,return,switch,synchronized,short,static,super,try,true,this,throw,throws,threadsafe,transient,void,while");
        int length = arrStr.length;
        for(int i=0; i<length; ++i) {
            System.out.print("/"" + arrStr[i] + "/"" + ",");
        }
        System.out.println();
    }
}

import java.util.*;
public class RE {
    public static void main (String[] args) {
        String[] keyword = new String[] {"abstract","break","byte","boolean","catch","case","class","char","continue","default","double","do","else","extends","false","final","float","for","finally","if","import","implements","int","interface","instanceof","long","length","native","new","null","package","private","protected","public","return","switch","synchronized","short","static","super","try","true","this","throw","throws","threadsafe","transient","void","while"};
        Scanner in = new Scanner(System.in);
        p("Input String:");
        String str = in.next();
        boolean flag = true;
        for(int i=0; i<keyword.length; ++i) {
            if(str.equals(keyword[i])) {
                flag = false;
                break;
            }
        }
        if(false == flag) {
            p("It's NOT a Java identifier!");
        } else {
            String regEx = "[$a-zA-Z][$//w]*";
            if(str.matches("[$a-zA-Z][$//w]*")) {
                p("This is a Java identifier!");
            } else {
                p("It's NOT a Java identifier!");
            }
        }
    }
    public static void p (String s) {
        System.out.println(s);
    }
}