How Can I Convert a String to Compilable Java Code and Use It For Dynamic Code Generation?

String comparableClassName = ...; // the class name of the objects you wish to compare
String comparatorClassName = ...; // something random to avoid class name conflicts
String source = "public class " + comparatorClassName + " implements Comparable<" + comparableClassName + "> {" +
                "    public int compare(" + comparableClassName + " a, " + comparableClassName + " b) {" +
                "        return " + expression + ";" +
                "    }" +
                "}";

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

// Please refer to the JavaCompiler JavaDoc page for examples of the following objects (most of which can remain null)
Writer out = null;
JavaFileManager fileManager = null;
DiagnosticListener<? super JavaFileObject> diagnosticListener = null;
Iterable<String> options = null;
Iterable<String> classes = null;
Iterable<? extends JavaFileObject> compilationUnits = new ArrayList<? extends JavaFileObject>();
compilationUnits.add(
    new SimpleJavaFileObject() {
        // See the JavaDoc page for more details on loading the source String
    }
);

compiler.getTask(out, fileManager, diagnosticListener, options, classes, compilationUnits).call();

Comparator comparator = (Comparator) Class.forName(comparableClassName).newInstance();