Magnolia 4.5 reached end of life on June 30, 2016. This branch is no longer supported, see End-of-life policy.
You need a Java Development Kit (JDK) for developing and deploying Magnolia. See the certified stack for supported Java versions. Check the version of Java SE installed on the platform where you plan to develop.
You may already have a Java Runtime Environment (JRE) installed on your machine but you need JDK for development.
To download Java SE: