private static String join(String str, int times, String sep) {
    	StringBuilder sb = new StringBuilder();
    	for(int i = 0; i < times; i++) {
    		sb.append(str);
    		if(i < times - 1) {
    			sb.append(sep);
    		}
    	}
    	return sb.toString();
    }
private static String join ( String str , int times , String sep ) { StringBuilder sb = new StringBuilder ( ) ; for ( int i = 0 ; i < times ; i ++ ) { sb . append ( str ) ; if ( i < times - 1 ) { sb . append ( sep ) ; } } return sb . toString ( ) ; }
例如：str=?,times=3,sep=,  返回 ?,?,?