Types, Values, and Variables - The Java Language Specification - page 45

4.2.5. The boolean Type and boolean Values
The boolean type represents a logical quantity with two possible values, indicated by the lit-
erals true and false (§ 3.10.3 ).
The boolean operators are:
• The relational operators == and != (§ 15.21.2 )
• The logical complement operator ! (§ 15.15.6 )
• The logical operators & , ^ , and | (§ 15.22.2 )
• The conditional-and and conditional-or operators && (§ 15.23 ) and || (§ 15.24 )
• The conditional operator ? : (§ 15.25 )
• The string concatenation operator + (§ 15.18.1 ) , which, when given a String operand
and a boolean operand, will convert the boolean operand to a String (either "true" or
"false" ), and then produce a newly created String that is the concatenation of the two
strings
Boolean expressions determine the control flow in several kinds of statements:
• The if statement (§ 14.9 )
• The while statement (§ 14.12 )
• The do statement (§ 14.13 )
• The for statement (§ 14.14 )
A boolean expression also determines which subexpression is evaluated in the conditional ?
: operator (§ 15.25 ).
Only boolean and Boolean expressions can be used in control flow statements and as the first
operand of the conditional operator ? : .
An integer or floating-point expression x can be converted to a boolean , following the C lan-
guage convention that any nonzero value is true , by the expression x!=0 .
An object reference obj can be converted to a boolean , following the C language convention
that any reference other than null is true , by the expression obj! =null .
A boolean can be converted to a String by string conversion (§ 5.4 ).
A cast of a boolean value to type boolean or Boolean is allowed (§ 5.1.1 , § 5.1.7 ) . No other casts
on type boolean are allowed.