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javastrong-typing

Java breaks strong typing! Who can explain it?

Possible Duplicate:
Varying behavior for possible loss of precision

I found an inconsistence in Java strong typing check at compile time. Please look at the following code:

int sum = 0;
sum = 1; //is is OK
sum = 0.56786; //compile error because of precision loss, and strong typing
sum = sum + 2; //it is OK
sum += 2; //it is OK
sum = sum + 0.56787; //compile error again because of automatic conversion into double, and possible precision loss
sum += 0.56787; //this line is does the same thing as the previous line, but it does not give us a compile error, and javac does not complain about precision loss etc.

Can anyone explain it to me? Is it a known bug, or desired behavior? C++ gives a warning, C# gives a compile error.

Does Java breaks strong typing? You can replace += with -= or *= - everything is acceptable by a compiler.

Solution

  • This behaviour is defined by the language (and is therefore OK). From the JLS:

    15.26.2 Compound Assignment Operators

    A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T)((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once. For example, the following code is correct:

    short x = 3;
x += 4.6;

    and results in x having the value 7 because it is equivalent to:

    short x = 3;
x = (short)(x + 4.6);