validation - Java - validating a subject Code -

i have subject code e.g: abc123 string

i need ensure of length 6, first 3 characters letters , last 3 numbers.

i try , in if statement? can work length cannot figure out numeric , letter part of things. e.g:

public void isvalidcode(string subjectcode2){     str = subjectcode2;     if (str.length() == 6 && """"need test others here??""" ) {         system.out.println("the code valid");     }     else {         system.out.println("the code not valid");     } 

you can use regular expressions, , matches() method of string class.

if (str.matches("[a-za-z]{3}[0-9]{3}")) {     // validation succeeded } else {     // validation failed }