Consider that you have a JDK version jdk1.8.0_191 installed on your machine. When you install and configure an Oracle Fusion Middleware product, the utilities, such as Configuration Wizard (
config.sh|exe), OPatch, or RCU point to a default JDK, for example, jdk1.8.0_191. After some time, Oracle releases a new version of the JDK, say jdk1.8.0_211 that carries security enhancements and bug fixes. You can upgrade the existing JDK to a newer version, and can have the complete product stack point to the newer version of the JDK.
You can maintain multiple versions of JDK and switch to the required version on need basis.