“bool” is an invalid keyword. Therefore, 1 and 4 can't be right. (Although 1 could be right if bool were a user-defined class but as per Java coding conventions, a class name should start with a capital letter.)

boolean b = 1; is wrong because you can only assign true or false to a Boolean variable. 1 is an integral value it cannot be converted to boolean. Also, note that boolean b = null; would be invalid as well because null is not a true or false value. A primitive (whether it is a boolean or an int or a double), can never be assigned null.

boolean b = true|false; and boolean b = true||false; are both valid and the difference between true|false and true||false is not material in this case. However, there is a lot of difference between | (and &) and || (and &&) as explained below:

|| and && perform short circuit evaluation, while & and | do not. Which means, if you use the || and && forms, Java will not bother to evaluate the right-hand operand if the result of the expression can be known by just evaluating the left hand operand.

Consider the following example:

Boolean b = true;
if(b || foo.timeConsumingCall()) {
//entered here without calling timeConsumingCall()
}

Another example:

String s = null;
if(s != null && s.isEmpty())       //No NullPointerException because string.isEmpty() is not called.
//If you use & instead of && , s.is Empty will be called and a
NullPointerException will be thrown.{
...
}