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Message:

Boolean Expressions

Posted by Isa Leshko on July 16, 2000 at 11:42 AM

> Can anyone tell me---
> else if (inTokens.countTokens( )>= 4) -- Why does this work
> else if (inTokens.countTokens( )>= 4 && <=5) -- But not this??
> Alison Lukstin Australia

In Java, the logical and operator (&&) compares the values
of two boolean expressions. It requires two operands to its left and
right that must be legal boolean expressions.

<=5 is not a legal boolean expression. Like &&, <= is a binary
operator that requires a value to its left and a value to its right.
You cannot <= 5 is lacking a left-hand operand.

On the surface, it may seem convenient to implicitly
reference an operand from the previous boolean expression.
However, this practice could lead to code that is difficult
to read and interpret for both human eyes and for javac

Let's take your example:
inTokens.countTokens( )>= 4 && <=5

Should <= compare 4 or inTokens.countTokens() relative to 5?

For more details on complex boolean expressions, check out
a lecture I have written on the subject:

http://www.people.fas.harvard.edu/~ileshko/CSCIE-50a/notes/notes-complex-boolean-expressions.html

It is linked off the site I maintain for my students:
http://www.people.fas.harvard.edu/~ileshko/CSCIE-50a/

HTH,
Isa