What is the difference between automatic promotion and casting in java?

[remote thicket]

Hello guys, I was just reading a bit about automatic promotion and casting in java. From what I have noticed, automatic promotion is always done implicitly by java compiler. So we won't see something like:

int num1 = 10;
double num2 = (double) num1;

While casting can be done implicitly or explicitly. I'm confuse here, what does this mean? I read that we can either change data type from a "bigger" data type to a smaller one or vice-versa. When do we need to explicitly mention the data type and why please

[wintry lark]

<@&987246399047479336> please have a look, thanks.

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TJ-Bot

Hello guys, I was just reading a bit about automatic promotion and casting in java. From what I have noticed, automatic promotion is always done implicitly by java compiler. So we won't see something like: ```java int num1 = 10; double num2 = (double) nu

n is the process in which smaller data types are automatically promoted to larger data types during arithmetic operations, while casting is the explicit conversion of a variable from one data type to another.

Automatic promotion occurs when two operands of different data types are involved in an arithmetic operation. In this case, the smaller data type is automatically promoted to the larger data type before the operation is performed. For example, if you have an int and a double being added together, the int will be automatically promoted to a double before the addition takes place.

Casting, on the other hand, is when you explicitly tell Java to convert a variable from one data type to another. This can be useful when you want to assign a value of one data type to a variable of another data type. For example, if you have a double and you want to store it as an int, you would need to cast it like this: int myInt = (int) myDouble;

In summary, automatic promotion happens automatically during arithmetic operations between different data types, while casting requires explicit conversion from one data type to another.

- AI generated response

[dusky geode]

you need explicit cast when for primitive there is possible data loss, for reference types when it is an unsafe cast

[hollow cove]

It should be noted that casting means two things in Java - for reference types there no 'change' happening, it's just type information for the compiler (and it will insert a check in the byte-code to ensure you aren't making a false assumption.

For primitives it's a type conversion - changing the size and/or format of the data.

This is often referred to as widening and narrowing. Nominally widening is lossless, narrowing usually isn't and you must explicitly narrow a type with a cast.

[remote thicket]

hmm when do we say a cast is "unsafe" please, this has to do with inheritance?

[remote thicket]

hmm what do you mean there is "no change happening" for reference type please

[dusky geode]

If you try to cast Dog to Animal, it works fine, it's implicit or "automatic" like you said
If you try to cast Animal to Dog, nothing said that the Animal was a Dog, so it's unsafe, and so you need to tell java "I'm sure of what I am doing"
Note that you should never do casts in this direction in OOP

[dusky geode]

Cast for reference types only change the way you see the objects.
There is the type hint and the actual type basically
If you have Animal animal = ... here Animal is an hint, the actual type of the object could be any Animal, like a Dog for example

[remote thicket]

oh ok I see. So we can say that:

Casting with referenced type doesn't change their actual type but rather their type hint

If we try to cast an object which is of a generic type, consider the following example:

Animal myAnimal = new Animal();
Dog myDog = (Dog) myAnimal // will result into a cast exception

Notice that we get a classCastException. This is because, we explicitly say to the compiler to consider myAnimal as an instance of a Dog but this isn't the case, myAnimal is an instance of a generic type, Animal.

When we preprend (Dog) as a prefix, it just changes type hint, not the actual type