Enthuware

You cannot build Java applications for smartphones such as Android/iOS using Java SDK because Oracle has not created a Java SDK version for these operating systems.

Java ME stands for Java Platform, Micro Edition. This is a trimmed down version of Java Standard Edition (Java SE) that is meant to develop applications for small consumer devices such as the ones used in the "Internet of Things". This includes devices ranging from TVs and Washing machines to micro-controllers such as Raspberry Pi. The Java ME specifications are designed to be rich in functionality, portable to a wide range of devices, flexible, and secure while being very resource-efficient and keeping the demands on the underlying platform low. Since such devices have too few resources as compared to desktop and server machines, Java ME provides a substantially reduced set of features as compared to Java SE. Just like you need Java SDK to build regular Java applications, you need Java ME SDK to build applications for such devices. The Java ME SDK is actually called "Java ME Embedded". Java ME Embedded provides the implementation of the Java ME specifications.