Object-Oriented Introduction to Java - Multimedia Introduction to Programming Using Java - page 20

• Conjunction, or and : b1 && b2
Expression b1 && b2 evaluates to true if both b1 and b2 are true and
evaluates to false otherwise. Operands b1 and b2 are called conjuncts .
• Disjunction, or or : b1 || b2
Expression b1 || b2 evaluates to true if either b1 or b2 (or both) is
true and to false otherwise. Operands b1 and b2 are called disjuncts .
For example, we evaluate the expression true && !( false || false ) :
1. false || false evaluates to false ,
so the expression becomes true && ! false .
2. !false evaluates to true ,
so the expression becomes true && true .
3. true && true evaluates to true .
You are not likely to use operations ! , && , and || very much in the begin-
ning. However, we need type boolean in order to talk about arithmetic relations ,
which yield boolean values. Assuming that e1 and e2 are both int or double
expressions, we can use the following arithmetic relations:

e1 < e2 true if e1 is less than e2 and false otherwise.
e1 > e2 true if e1 is greater than e2 and false otherwise.
e1 <= e2 true if e1 is at most e2 and false otherwise.
e1 >= e2 true if e1 is at least e2 and false otherwise.
e1 == e2 true if e1 and e2 are equal and false otherwise.
e1 != e2 true if e1 and e2 are different and false otherwise.
For example, the expression 5+3<9 evaluates to true , and 5+3<8 eval-
uates to false . The operators < , > , <= , >= , == , and != are called relational oper-
ators .
Be careful with equality: The phrase 5=6 is not a Java expression! Java uses
the sign == for an equality test, rather than = , and uses = in another way, which
we describe in Sec. 1.2. For example, 6==6 evaluates to true and 5==6 eval-
uates to false . This breaking of mathematical convention is unfortunate. For
hundreds of years, ever since Robert Recorde introduced the sign = for equality
in the 1600s, that convention has been in use. To have programming languages
break with that tradition is a travesty.

Operator Operation Example Result

not , or negation

! ! true false

and , or conjunction

&& true && false false

or , or disjunction

|| true || false true

Figure 1.2: Basic boolean operators in Java