boolean : Java Glossary

by Roedy Green ©1996-2008 Canadian Mind Products
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boolean

Java has a logical type that can only have the values true or false called boolean. The boolean type deals with only a single bit at a time. An immutable object wrapper around a boolean is called a Boolean. You can do boolean operations on ints or longs, many bits at a time using &, |, ^ and ~. With boolean, you can only process one bit at a time, typically with !, && and ||. For bit strings longer than 64 bits, use java. util. BitSet. Even experienced programmers sometimes lapse into redundant newbie-like baby talk when using booleans. To avoid that embarrassement see newbie.

boolean expressions

Anything you can put inside an if (...) is a boolean expression e.g.

// example boolean expressions
x > 2
0 <= y && y <= 10
! (0 <= y && y <= 10 )
button.isVisible()

A boolean expression evaluates to true or false. You can store it in a boolean variable e.g.

// storing a boolean expression in a variable
boolean whether = x > 2;

You can print out a boolean variable. You don’t need an if to do it.

// displaying a boolean variable on the console
System.out.println( whether );

You can use a boolean variable in an if later rather than recalculating the expression.

// referencing a boolean variable in an if
if ( whether ) makeDate();
if ( ! whether && done() ) finish();

boolean vs int

In C, booleans and ints are pretty well interchangeable. In Java they are totally separate types. You can’t do the following in Java:

// ILLEGAL IN JAVA!!  int is not the same as boolean
int seen = button.isVisible();
if ( seen ) doSomething();

You must write:

// boolean must be used in Java where in C you could use an int.
boolean visible = button.isVisible();
if ( visible ) doSomething();

// or using an int with int-style syntax.
int seen = button.isVisible() ? 0 : 1;
if ( seen != 0 ) doSomething();

& vs && and | vs ||

&& and || are sometimes called short circuit & and | or McCarthy & and |.

Stuttering

Avoid goony expressions like:

// Goony stuttering code often written by newbies

if ( whether == true )

// or

if ( whether == false )

// or

if ( whether == true && done == false )

Don’t stutter, just write:

// terse code

if ( whether )

// or

if ( !whether )

// or

if ( whether && !done )

binary
bit
masking
newbie

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