The reason for the replacement is a matter of debate among developers and industry observers, but most agree that there are technical benefits to the change. Still, many folks point to the Oracle vs. Google lawsuit, and say Google is making concessions to settle the lawsuit and head off possible future claims. Whatever the reason, Android N, the codename for the next major version of Android, will be based on OpenJDK.
Apache Harmony is an open-source, “clean room” implementation of Java developed by the Apache Software Foundation. OpenJDK is Oracle’s free and open-source implementation of Java, licensed under the GNU General Public License (GNU GPL) with a linking exception.
Oracle closed its acquisition of Sun Microsystems in January 2010 and in August of that same year, it sued Google for copyright and patent infringement over Google’s use of Java in Android. At issue was the improper use of Java APIs, Oracle claimed. However, Google argued that APIs could not be copyrighted and eventually won its case in a 2012 jury verdict. Yet, in 2014 another court partially reversed the prior ruling to side with Oracle. The case is ongoing and the legal battle rages on -- as does the fight over developer mindshare.
Indeed, Java 8 brought with it enhanced developer productivity and significant application performance increases through reduced boilerplate code, improved collections and annotations, simpler parallel programming models and more efficient use of modern, multicore processors. Thus, the move to OpenJDK brings Java 8 support and also simplifies the Android code by providing a common code base for development.