Java Reference

In-Depth Information

Java calls this kind of variable a
boolean
,
5
and it can be assigned
true
or
false
,

or you can give it math expressions using any of these operators, all of which

return either
true
or
false
:

Equal to
(two equals signs)

==

!=

Not equal to

!

Not
(so “not true” is false, and “not false” is true)

<

Less than

>

Greater than

Less than or equal to

<=

>=

Greater than or equal to

&&

And
(true if both things are true)

||

Or
(true if either thing is true)

For example, given these variables

int
a = 10;

int
b = 5;

String
h =
new String
(
"Hello"
);

boolean
result = true;

boolean
badone = false;

Java will figure out these comparisons:

•
a==10
is
true

•
b==6
is
false

•
a<20
is
true

•
b>=5
is
true

•
a>100
is
false

•
result
is
true

•
!result
is
false
(pronounced “not result”—“not” returns the opposite of a value)

•
result&&badone
is
false
(pronounced “and”—true only if both are true)

•
result||badone
is
true
(pronounced “or”—true if either is true)

But this next one won't do what you think it should; it will not be
true
:

h ==
"Hello"
;
// Gotcha!

That one is tricky. For strings and objects (more on that in the next chapter),

use the
equals
function instead of the double equals sign (
==
), like this:

h.equals(
"Hello"
);

// is true

5.

Named for George Boole, the British mathematician, who came up with these ideas in

the 1800's.