Boolean data type

The Boolean data type represents 0 (false) or 1 (true).
The computer is able to test the inequality or equality true or false.

Using Boolean Expressions: Predicate Method

• A predicate method returns a boolean value

  public boolean isOverdrawn()

  {

     return balance < 0;

  }

• Use in conditions

  if (harrysChecking.isOverdrawn())

• Useful predicate methods in Character class:

  isDigit

  isLetter

  isUpperCase

  isLowerCase

• if (Character.isUpperCase(ch)) . . .

• Useful predicate methods in Scanner class:
  hasNextInt() and hasNextDouble()

  if (in.hasNextInt()) n = in.nextInt();

AND & OR & NOT

AND  (&&):
If there are two events joined by AND, both events have to be true for the result of join to be true.
For example, if x is between 100 and 200, you can write if (x >100 && x <200) ...

OR ( || )
If there are two events joined by OR, both events have to be false for the result of join to be false.
For example, if input can be 's' or 'S', you can write if (input == 's' || input == 'S') ...

NOT ( !)
Opposite of the original.

Using Boolean Variables

• private boolean married;

• Set to truth value:

married = input.equals("M");

• Use in conditions:

  if (married) . . . else . . . if (!married) . . .

It is considered gauche to write a test such as

  if (married == true) . . . // Don't
if (character.isDigit(ch) == false) . . . // Don't

Just use the simpler test

  if (married) . . .
if (!Character. isDigit(ch)) . . .