Just to be clear, there "Java" is not one thing.
Java Runtime Environment (JRE) - the most common form of Java, allows applications written in Java to run on your computer. This is the "java plugin" or the "java virtual machine (jvm)"
Java (the language) - an object oriented programming language.
Java (the compiler) - turns Java code (language) into class files that can be executed by the JRE/JVM.
Java (the library) - a set of components for cross-platform GUI and other programming elements.
I assume you're asking about replacing the JRE, the Java plugin that most people use. If you mean otherwise, please update your question.
Microsoft used to have a Java Virtual Machine included on all their OSes, but that is usually ignored in favor of a JRE plugin from Oracle.
There are a few other JRE/JVM replacements you can try:
JOEQ (ironically enough itself written in Java) - http://sourceforge.net/projects/joeq/
Wonka - http://wonka.acunia.com/
Sable (no longer actively maintained) - http://sourceforge.net/projects/sablevm/files/
Each of these may have some amounts of compatibility, but you'll probably find when running Java meant for a newer version of the JRE, you may run into compatibility issues.
Something else to consider is whether or not you really need Java. Are there specific tasks you do that actually explicitly require JRE to run? If not, try going without it.