Home/ Questions/Q 8584819
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-11T21:51:43+00:00

I know I can use the comma operator like this for (int i =

  • 0

I know I can use the comma operator like this

for (int i = 1, j = 15; j>10; i++, j--) {
    // do something neat
}

but some articles seem to suggest that the comma operator can be used outside of the for loop declaration, for example

int j = 2, k = 4 ;
int x ;
// Assignment statement with comma operator
x = j + 1, k ;

source: http://www.cs.umd.edu/~clin/MoreJava/ControlFlow/comma.html

or

int x = (expression) ? (i++,2) : 3;

source: https://stackoverflow.com/a/12047433/1084813

This would be a neat trick for a code obfuscation contest or to confuse my colleagues, but neither of the examples will compile (Java 1.6, Eclipse Juno), the error is “The left-hand side of an assignment must be a variable”. I tried looking at the compiler settings to see whether it could be forbidden to prevent bad code, but without luck.

What’s wrong? Was the comma operator a part of an older specification which later changed? Are the people that wrote those examples using a different Java setup that allows this?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    What’s wrong?

    Some of the tricks which work in C don’t work in Java.

    Was the comma operator a part of an older specification which later changed?

    This never worked in Java AFAIK.

    Are the people that wrote those examples using a different Java setup that allows this?

    Its a common mistake to assume Java is just like C or C++ because it is similar. A good portion of coding mistakes on SO are due to people trying to write C++ in Java and getting confused when it doesn’t do what they expect.

    BTW: I have made the same mistake assuming C++ is just like Java as my knowledge of C++ is not current.

    However some tricks which working Java but perhaps not C.

    You can use all currency symbols or which there are a few which look at most the same.

    e.g.

    if( ⁀ ‿ ⁀ == ⁀ ⁔ ⁀ || ¢ + ￠== ₡)

    You can use character which are invisible and c couple which reverse the order the rest of the line when printed. 😉

    This program compiles and runs and prints all the odd characters you can use in Java identifiers

    for (char c‮h = 0; c‮h < Character.MAX_VALUE; c‮h++)
    if (Character.isJavaIdentifierPart(c‮h) && !Character.isJavaIdentifierStart(c‮h))
        System.out.printf("%04x <%s>%n", (int) c‮h, "" + c‮h);

    which makes its almost too easy.

    http://vanillajava.blogspot.co.uk/2012/08/uses-for-special-characters-in-java-code.html

    http://vanillajava.blogspot.co.uk/2012/09/hidden-code.html

    • 0