Understanding narrowing primitive conversion

I'm trying to understand the narrowing primitive conversion concept in Java. Here's what the JLS 5.1.3 says about it:

22 specific conversions on primitive types are called the narrowing primitive conversions:

short to byte or char

char to byte or short

int to byte, short, or char

long to byte, short, char, or int

float to byte, short, char, int, or long

double to byte, short, char, int, long, or float

Since there is the implicit conversion converting long to int, we can write the following code:

public static void main (String[] args) throws java.lang.Exception
{
    int c = 88L; //Compilation fail
    System.out.println(c);
}

DEMO

But it doesn't work. Why? The narrowing conversion from long to int should have been applied.

Jon Skeet
people
quotationmark

Since there is the implicit conversion converting long to int

There isn't. There's an explicit conversion. Narrowing conversions aren't generally applied implicitly, precisely because they can lose information. So you'd need:

int c = (int) 88L;

Indeed, the initial part of JLS section 5 even gives an example:

// Casting conversion (5.4) of a float literal to
// type int. Without the cast operator, this would
// be a compile-time error, because this is a
// narrowing conversion (5.1.3):
int i = (int)12.5f;

There are some cases where narrowing conversions are applied explicitly in assignment contexts (JLS 5.2) though:

In addition, if the expression is a constant expression (ยง15.28) of type byte, short, char, or int:

  • A narrowing primitive conversion may be used if the type of the variable is byte, short, or char, and the value of the constant expression is representable in the type of the variable.

  • A narrowing primitive conversion followed by a boxing conversion may be used if the type of the variable is:

    • Byte and the value of the constant expression is representable in the type byte.

    • ... (similar for Short and Character)

That's why this is valid even though the type of the literal 120 is int:

byte x = 120;

Compare that with widening conversions, which are permitted within assignment contexts and invocation contexts (JLS 5.3).

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