Source taken from Sven Furuslätt; https://www.quora.com/How-can-I-dynamically-create-a-Java-class-and-execute-its-methods-at-runtime

DynamicClassCompilationAndExecution.java

// create an empty source file
File sourceFile = File.createTempFile("Hello", ".java");
sourceFile.deleteOnExit();

// generate the source code, using the source filename as the class name
String classname = sourceFile.getName().split("\\.")[0];
String sourceCode = "public class " + classname + "{ public void hello() { System.out.print(\"Hello world\");}}";

// write the source code into the source file
FileWriter writer = new FileWriter(sourceFile);
writer.write(sourceCode);
writer.close();

// compile the source file
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
File parentDirectory = sourceFile.getParentFile();
fileManager.setLocation(StandardLocation.CLASS_OUTPUT, Collections.singletonList(parentDirectory));
Iterable<? extends JavaFileObject> compilationUnits = fileManager.getJavaFileObjectsFromFiles(Collections.singletonList(sourceFile));
compiler.getTask(null, fileManager, null, null, null, compilationUnits).call();
fileManager.close();

// load the compiled class
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { parentDirectory.toURI().toURL() });
Class<?> helloClass = classLoader.loadClass(classname);

// call a method on the loaded class
Method helloMethod = helloClass.getDeclaredMethod("hello");
helloMethod.invoke(helloClass.newInstance());