first steps of the lexer

Exercise 5/Lexer.java

@@ -0,0 +1,9 @@
+public class Lexer {
+    Lexer(String src_in) {
+        System.out.println(src_in);
+    }
+
+    public void run() {
+        System.out.println("Lexer runs.");
+    }
+}