Question about Strings and Arrays

[Oliver Nono]

I just finished the Chapter 3 Self test in the Java 2 Certification book by Kathy Sierra and Bert Bates and I am a little confused on question 17. Basically the question is about this:
long [] a1 = {3, 7, 5}
long [] a2 = {3, 7, 5}
System.out.print(a1[0] + a1[1] + a1[2] + " ");
System.out.println(a2[0] + a2[1] + a2[2]);
What is the result?
The answer in the book says it is 15 15. But I thought that if there is any Strings included in a System.out.print statement it would concatenate what is in the array to print this:
375 15.
Please let me know where I am making the mistake. Thanks.

[Bryan Helm]

Each + is a binary operation (two operands) evaluated separately, and whether it is numeric addition or string concatenation is decided for each one separately. If either operand to a particular + is a String, it is evaluated as String concatenation. In the example, this is true only of the last + in the first print statement, so the other + operators are evaluated as numeric addition operators.
[ April 13, 2003: Message edited by: Bryan Helm ]

[Oliver Nono]

I see. Thanks for the help. That one was tricky!