To develop an application with Java, JDK (Java SE Development Kit) is required for development and runtime environment.
JDK is provided by Oracle without any charge. Anyone can donwload it.
In addition to JDK, eclipse which is one of IDE(Integrated Development Environment) is frequently used. It is better to install eclipse too.
Note that Android development environment is not required because eclipse will be installed when you install Android SDK.
Follow the steps below to construct a Java development environment.