CODEWITHSUNDEEP
javaoperators
Vivek
Vivek

Reputation: 493

short-circuiting behavior of conditional OR operator(||)

Both conditional operators && and || are short-circuited as per
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html, which means the second operand does not need to be evaluated at times.

Could somebody please provide an example in which the conditional-OR(||) operator would be short-circuited?

Short-circuiting behavior is pretty straightforward with the conditional-AND(&&) operator as in:

if(false && (1 > 0)) then the second operand:(1 >0) would not need to be evaluated but can't seem to find/think of an example for conditional-OR.

Upvotes: 17

Views: 2679

Answers (3)

Adam Mihalcin
Adam Mihalcin

Reputation: 14478

The or operator is short-circuited when the first operand is true. So,

String foo = null;
if (true || foo.equals("")) {
    // ...
}

doesn't throw a NullPointerException.

As @prajeesh rightly points out in the comments, on way that short-circuiting is used in real code is to prevent a NullPointerException whenever you are dealing with an API that might return null. So, for instance, if there is a readStringFromConsole method that returns either the currently available string or null if the user doesn't type anything, we could write

String username = readStringFromConsole();
while (username == null || username.length() == 0) {
    // No NullPointerException on the while clause because the length() call
    // will only be made if username is not null

    System.out.println("Please enter a non-blank name");
    username = readStringFromConsole();
}

// Now do something useful with username, which is non-null and of nonzero length

As a side note, an API that returns user input should return the empty string whenever the user doesn't type anything, and shouldn't return null. Returning null is a way of saying "there is nothing available," while returning the empty string is a way of saying "the user didn't type anything" and so is preferred.

Upvotes: 22

lrAndroid
lrAndroid

Reputation: 2854

if (true || comparison)

comparison will never be evaluated, since its result is irrelevant (because the first argument is already true).

Upvotes: 1

scientiaesthete
scientiaesthete

Reputation: 929

if(true || (0 > 1))

The first statement is true, and so it is not necessary to evaluate the second.

Upvotes: 1

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