Conditional Structures and Loops - A Concise and Practical Introduction to Programming Algorithms in Java - page 37

< less than
<= less than or equal to
> greater than
>= greater than or equal to
== equal to
!= not equal to

One of the most frequent programming errors is to use the equality symbol =
instead of the relational operator == to test for equalities:

int x=0;

if (x=1) System.out.println("x equals 1");
else System.out.println("x is different from 1");

Fortunately, the compiler generates an error message since in that case types
boolean/int are incompatible when performing type checking in the expression
x=1 . But beware that this will not be detected by the compiler in the case of
boolean variables:
boolean x=false;
if (x=true) System.out.println("x is true");
else System.out.println("x is false");

In that case the predicate x=true contains an assignment x=true and the
evaluated value of the “expression” yields true , so that the program branches
on the instruction System.out.println("x is true"); .
A boolean predicate may consist of several relation operators connected using
logical operators from the table:

&& and
|| or
!

not

The logic truth tables of these connectors are given as:

||

&& true false
true true false
false false false

true false
true true true
false true false

Whenever logical operators are used in predicates, the boolean expressions are
evaluated in a lazy fashion as follows:

- For the && connector, in Expr1 && Expr2 do not evaluate Expr2 if Expr1
is evaluated to false since we alreaady know that in that case that Expr1
&& Expr2 = false whatever the true/false outcome value of expression
Expr2 .