Abhinandan Abhinandan - 2 months ago 12
Groovy Question

difference between int and Integer type in groovy

I have just started learning groovy and I am reading "Groovy in Action".
In this book I came across a statement that it doesn’t matter whether you declare or cast a variable to be of type int or Integer.Groovy uses the reference type ( Integer ) either way.

So I tried to assign null value to a variable with type int

int a = null


But it is giving me below exception


org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'null' with class 'null' to class 'int'. Try 'java.lang.Integer' instead
at Script1.run(Script1.groovy:2)


Then I tried to assign null value to a variable with type Integer

Integer a = null


and it is working just fine.

Can anyone help me understand how
groovy
behaves such way or the reason behind it?

Answer

The core problem is that primitives can’t be null. Groovy fakes that out with autoboxing.

If you store a null value in a number, you can’t store that in a int/long/etc field. It’s not correct to convert a null number to 0, since this might be valid values. Null means that no value or choice has been made yet.

int is a primitive type and it is not considered as an object. Only objects can have a null value while int value can't be null because It's a value type rather than a reference type

For primitive types, we have fixed memory size i.e for int we have 4 bytes and null is used only for objects because there memory size is not fixed.

So by default we can use :-

int a = 0
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