What is the difference between double a = a + int b and int a += double b?

Question

Why does:

public class Addition {    public static void main() {      int a = 0;      double b = 1.0;      a = a + b;     System.out.println(a);    } } 

not compile but:

public class Addition {    public static void main() {      int a = 0;      double b = 1.0;      a += b;      System.out.println(a);    } } 

compiles.

Answer 1

In Java += operator has an implicit cast to the left hand type. This goes for all composed operators.