New Integer vs valueOf

Question

I was using Sonar to make my code cleaner, and it pointed out that I'm using new Integer(1) instead of Integer.valueOf(1). Because it seems that valueOf does not instantiate a new object so is more memory-friendly. How can valueOf not instantiate a new object? How does it work? Is this true for all integers?

Answer 1

Integer.valueOf implements a cache for the values -128 to +127. See the last paragraph of the Java Language Specification, section 5.1.7, which explains the requirements for boxing (usually implemented in terms of the .valueOf methods).

http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.1.7