Cay grew up in Northern Germany. As per concern the education of Cay, he received a M.S. in computer science from Syracuse University. After that he did his Ph.D. in mathematics from the University of Michigan in Ann Arbor.

Cay started his career in 1986 as a President of Horstmann Software Design Corporation. Very soon in 1987 Cay joined San Jose State University as a Professor of Computer Science till now. In 1997 Cay joined Preview Systems Inc. as a Vice President and Chief Technology Officer till 2000. Now He is a computer science series editor at Prentice-Hall.

Cay is a very good writer for java too. He wrote many famous books on java like Core Java of Sun Microsystems Press, Core JavaServer Faces, BigJava, Java Concepts and Object-Oriented Design & patterns.  

Cay is also active in many professional activities is a Series Editor for the Prentice-Hall Core Computing Series. Cay is appointed as a member of the Development Committee for the College Board Advanced Placement Computer Science Examination from 2004 to 2008. Cay took part in the Intel International Science and Engineering Fair, 2001 as a judge. He is an Advisory Board Member in Visual Numerics Inc.