CODEWITHSUNDEEP
if-statementgroovy
Jakov
Jakov

Reputation: 999

Why does 0 integer value behaves as false in if statement in groovy?

I wrote this part of code.

Integer value = 0

if(value) {
    print "true"
} else {
    print "false"
}

And the output of code is false. Can someone explain me why does Integer 0 value behaves as false in this if statement when it is not null and it exists?

Upvotes: 3

Views: 5532

Answers (2)

Szymon Stepniak
Szymon Stepniak

Reputation: 42194

When Groovy sees a variable in the context where a boolean value is expected, it invokes DefaultGroovyMethods.asBoolean(object) method to coerce given value to its boolean representation. For numbers following code gets executed:

/**
 * Coerce a number to a boolean value.
 * A number is coerced to false if its double value is equal to 0, and to true otherwise,
 * and to true otherwise.
 *
 * @param number the number
 * @return the boolean value
 * @since 1.7.0
 */
public static boolean asBoolean(Number number) {
    return number.doubleValue() != 0;
}

Source: src/main/org/codehaus/groovy/runtime/DefaultGroovyMethods.java

That is why Groovy coerce 0 to false and any non-zero number to true.

There are other coercions that Groovy mades for you, e.g. empty list coerces to false, empty string coerces to false etc. I have written an article about some of them, you might find it useful.

Upvotes: 9

cfrick
cfrick

Reputation: 37033

It's part of the "Groovy Truth"

5.7. Numbers

Non-zero numbers are true.

assert 1
assert 3.5
assert !0

Upvotes: 5

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