Java: Why a += b does not give any compile error while a = a + b does when a is int and b is double?

Question

In Java
I am using statement a += b where a is int and b is double, when I use a += b, it won't give error but in case of a = a + b it gives error, why ?

Answer 1

When You use a += b in Java, the interpreter changes your statement a += b to
a = (instanceof a) (a + b) i.e. it automatically typecasts your assignment so no error came but when you write a = a + b; it needs an explicit typecast.

so if you write,

int a = 3;
a += 32.5;    //    it actually a = (int)(a + 32.5);