boolean keyword

Description
The boolean type represents a logical quantity with two possible values, indicated by the literals true and false. Boolean literals can be used to test a positive or negative state, or to declare the only possible values for a boolean variable.

The boolean operators are:

The string concatenation operator + converts 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: if, while, do, and for. A boolean expression also determines which subexpression is evaluated in the conditional ? : operator.

A cast of a boolean value to type boolean is allowed; no other casts on type boolean are allowed.

Examples
You can declare a boolean variable, and give it an initial value when you declare it:

boolean okToContinue = true; 

You can use a boolean expression to determine control flow:

if (okToContinue && (a < b)) { 
    ...
}

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Java types
do keyword
for keyword
if keyword
while keyword

Source: The Java Language Specification. Copyright (C) 1996 Sun Microsystems, Inc.