Why variable names in Java cannot have same names as keywords?

In most programing languages that I know you cannot declare a variable with name that is also a key word.

For example in Java:

public class SomeClass
{
    Class<?> clazz = Integer.class; // OK.
    Class<?> class = Integer.class; // Compilation error.
}

But it's very easy to figure out what is what. Humans reading it will not confuse variable name with class declaration and compiler will most likely not confuse it too.

Same thing about variable names like 'for', 'extends', 'goto' or anything from Java key words if we are talking about Java programming language.

What is the reason that we have this limitation?

What is the reason that we have this limitation?

There are two reasons in general:

• As you identified in your Question: it would be extremely confusing for the human reader. And a programming language that is confusing by design is not going to get significant traction as a practical programming language.

• If identifiers can be the same as keywords, it makes it much more difficult to write a formal grammar for the language. (Certainly, a grammar like that with the rules for disambiguation cannot be expressed in BNF / EBNF or similar.) That means that writing a parser for such a language would be a lot more complicated.

Anyhow, while neither of these reasons is a total "show stopper", they would be sufficient to cause most people attempting a new programming language design / implementation to reject the idea.

And that of course is the real reason that you (almost) never see languages where keywords can be used as identifiers. Programming language designers nearly always reject the idea ...

(In the case of Java, there was a conscious effort to make the syntax accessible to people used to the C language. C doesn't support this. That would have been a 3rd reason ... if they were looking for one.)

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There is one interesting (semi-) counter example in a mainstream programming language. In early versions of FORTRAN, spaces in identifiers were not significant. Thus

    I J = 1

and

    IJ = 1

meant the same thing. That is cool (depending on your "taste" ...). But compare these two:

    DO 20 I = 10, 1, -2

versus

    DO 20 I = 10

One is an assignment, but the other one is a "DO loop" statement. As a reader, would you notice this?