The tool that allow you write JVM instruction using assemble like command

http://jasclipse.sourceforge.net/

An article about assemble Java - http://www.theserverside.com/tt/articles/content/GuideJavaBytecode/article.html

Overview of bytecode - http://arhipov.blogspot.com/2011/01/java-bytecode-fundamentals.html http://www.javaadvent.com/2013/12/mastering-java-bytecode.html https://blog.jamesdbloom.com/JavaCodeToByteCode_PartOne.html