add java version lexer as in book,not tested yet.
	new file:   2.6/java_src/Lexer.java
	new file:   2.6/java_src/Num.java
	new file:   2.6/java_src/Tag.java
	new file:   2.6/java_src/Token.java
	new file:   2.6/java_src/Word.java