What makes the need for Jflex, as a lexical analyzer building tool, for the Java language?
Why Flex is not enough for the same task?
Kindly explain with example of a Java language construct being unable to be tokenised using flex.

P.S.: Am a trainer, so please delve into details for the above, as there can be many questions asked for the above, to me.

flex is written in c, jflex written in java. Otherwise google is your friend.
https://en.wikipedia.org/wiki/Compar...ser_generators

It just states the lexer algorithm, in a table, for a given compiler; but never states the language in which the lexer is implemented; unless you search the individual compiler.

My question would even then (after searching, for the individual compilers' details) would remain unanswered; i.e.:
Do the lexer need be coded in the same language as the source language?

To answer the original question: certainly not.

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Flex produces C or C++, which isn't very helpful for a developer who knows Java, but not C or C++ languages.

However, as per its manual, JFlex is not a Java version of Flex, it's a faster version of JLex.

Both Flex and JLex were inspired by Lex (which used to be proprietary software).

The language a lexer is implemented in is mostly irrelevant (except if it requires a particular VM to run), but they will often be implemented in the same language as the output language because that's a language the authors are comfortable working/developing with.

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The original question was: Does lexer tool need be coded in the same language, as the source language?

But, request examples, and theory justifying your answer.
Also, request in which cases, the constraint of the lexer being coded in the source language, is not applicable.

Um, have you not actually taken the course you're about to be teaching? I believe misread the use of the word "trainer" here. EDIT2: or not?

Regardless, following suggestion still applies:

Why don't you try to figure this out based on the definition of a lexer and tell us where you get stuck.

A lexer is an executable. You want an example of how it doesn’t matter what language an executable is compiled from?

Not to be rude, but this is something you should have thought about before asking.

EDIT: nevertheless, I found you an example. The Iexer is written in Java, and it’s used to analyze a program written in Kotlin.

http://db.science.uoit.ca/teaching/c...3_antlr_lexer/

As far as I know, lex is written in C, its source language is lex/C mix, its target language is C; jlex is written in Java, its source language is jlex/Java mix, its target language is Java.

You could write a Java program that has the functionality of lex, also you could write a C program that has the functionality of jlex.

Note: I guess the OP uses word 'trainer' for 'beginner', word 'request' for 'please give' etc.

These tools are designed to produce source-code to be incorporated into your compiler project. It is most convenient for most people for a tool which generates [Java] source-code to itself be written in [Java]. "Dance with the one who brung 'ya."

Oh, this makes sense actually. "Trainer" as in "one who is being trained", not "one who is doing the training of others" as I read it first.

Dear sir, am M.Tech.(CSE) from NIT-Warangal, based on 433 AIR in GATE; and had subject of Compiler Design, in that course.
Am a Lecturer now, and very soon, i.e. from today, the classes will start too, for the odd semester.

That is laudable.