CODEWITHSUNDEEP
javacompiler-errorsimplicit-conversion
Carlos Guedes
Carlos Guedes

Reputation: 143

implicit conversion in java operator +=

I've found that java compile has a non-expected behavior regarding assignment and self assignment statements using an int and a float.

The following code block illustrates the error. 

    int i = 3;
    float f = 0.1f;

    i += f;              // no compile error, but i = 3
    i = i + f;           // COMPILE ERROR

Can someone explain this behavior.

EDIT: I've posted this code block in https://compilr.com/cguedes/java-autoassignment-error/Program.java

Upvotes: 11

Views: 1705

Answers (2)

aviad
aviad

Reputation: 8278

i believe that the explicit i+f fails because of Narrowing primitive conversion. While in the first case the conversion on the right side passes because it is done according to Compound Assignment rules.

Upvotes: 0

Louis Wasserman
Louis Wasserman

Reputation: 198113

http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.26.2

The Java Language Specification says:

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.

So i += f is equivalent to i = (int) (i + f).

Upvotes: 11

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