boolean : Java Glossary

boolean expressions

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

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

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

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

boolean vs int

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

// 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 ||

Stuttering

Gotchas

• You can drive yourself crazy writing Java programs using booleans to represent pairs of states in a program i.e. busy vs active, ok vs error, Comparable vs Comparator, ascending vs descending where there is no blindingly obvious convention about which of the pair should be true and which false. The convention will not be obvious scaning the code. All you will see are trues and falses. It is very easy to accidentally reverse the convention on a method expecting the opposite convention. The compiler will not warn you. If you get a program half one convention and half the other you will have one heck of a time sorting it all out. What to do?
  • Use enums instead. You can hide the convention inside the enum, and use boolean getters with names like isAscending and isDescending on enum constants with names like ASCENDING and DESCENDING.
  • Using named static final boolean constants helps a little.
  • Make up some crazy mnemonic about which is which that will stick in your brain.
  • Use consistent variable and parameter names that make the convention obvious.