(a == b == true) or (a == true && b == true) ?

Question

if I had two booleans, 'a' and 'b', and I wanted to test for them both being true I have always used
if(a == true && b == true){
\\do somthing
but is
if(a == b == true){
\\do somthing
just as valid?
and efficient?
and what about
if(a == b != false){
\\do somthing

Answer 1

Just ramblin'....
I personally feel that using the notation (a == b == c), even if it turns out to mean exactly what you want to mean for a particular case, is a programming mistake because it differs from what a human automatically expects when he sees that "string of equals" notation. (Bravo to the writer of "use if(a &&b)" for saying it exactly like it was meant...)
From math we know that " (3+7)*4 = 40 = 12 + 28 ", because a "string of equals" is a statement that all of the members of the "string" are equivalent. So when we see (a == b == c) in a conditional expression in a program, don't we have the tendency to think of it as "a and b and c all have the same value" (i.e. all true or all false for booleans, all the same number for ints, ...)
In programming there is a different meaning to the "string of equals"; many beginning programmers mistakenly write this " if(a == b == 0) " when they mean this " if(a == 0 && b == 0) ".
...Of course java compiler catches that mistake (if a,b,c are not booleans), because (in the case of ints), this " if(a == b == 0) " is the same as this " if((a == b) == 0) " which written the latter way shows more clearly that it is trying to compare the equality of a boolean (a == b) and an int (0).
However, when a,b,c are boolean, the compiler doesn't complain, but it thinks different from the human math-trained brain. Out of curiosity + laziness, I wrote a little (redundant but simple) program to see some results...
Here is the output (with my later comment inserted with "--->'s):
(false == (false == false)) => false
((false == false) == false) => false
(false == false == false) => false
---> NOT Correct to the human-math-interpretation , all three are the same.
(false == (false == true)) => true
((false == false) == true) => true
(false == false == true) => true
---> NOT Correct to the human-math-interpretation , all three are NOT the same.
(false == (true == false)) => true
((false == true) == false) => true
(false == true == false) => true
---> NOT Correct to the human-math-interpretation , all three are NOT the same.
(false == (true == true)) => false
((false == true) == true) => false
(false == true == true) => false
---> Correct to the human-math-interpretation , all three are NOT the same.
(true == (false == false)) => true
((true == false) == false) => true
(true == false == false) => true
---> NOT Correct to the human-math-interpretation , all three are NOT the same.
(true == (false == true)) => false
((true == false) == true) => false
(true == false == true) => false
---> Correct to the human-math-interpretation , all three are NOT the same.
(true == (true == false)) => false
((true == true) == false) => false
(true == true == false) => false
---> Correct to the human-math-interpretation , all three are NOT the same.
(true == (true == true)) => true
((true == true) == true) => true
(true == true == true) => true
---> Correct to the human-math-interpretation , all three are the same.
Just ramblin'....
/Mel