Генерация класса из кода программы и последующая его компиляция - как?

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
 
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
 
public class LoadAndRun {
 
    public static void main(String[] args) throws IOException, ClassNotFoundException, InstantiationException,
            IllegalAccessException {
        String fileName = "MyClass.java";
        String className = "MyClass.class";
        File[] f = new File[] { new File(fileName), new File(className) };
        for (File file : f)
            file.delete();
 
        BufferedWriter fos = new BufferedWriter(new FileWriter(fileName));
        fos.write("public class MyClass { public String toString() { return \"MyClass running\"; } }");
        fos.flush();
        fos.close();
 
        JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager fileManager = javac.getStandardFileManager(null, null, null);
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
        Iterable<? extends JavaFileObject> compilationUnits1 = fileManager.getJavaFileObjectsFromFiles(Arrays
                .asList(new File[] { new File(fileName) }));
        javac.getTask(null, fileManager, diagnostics, null, null, compilationUnits1).call();
        for (Diagnostic diagnostic : diagnostics.getDiagnostics())
            System.out.println(diagnostic);
        fileManager.close();
        MyClassLoader loader = new MyClassLoader();
 
        Class my = loader.getClassFromFile(new File(className));
        Object o = my.newInstance();
        System.out.println(o.toString());
    }
 
    static class MyClassLoader extends ClassLoader {
 
        public Class getClassFromFile(File f) {
            byte[] raw = new byte[(int) f.length()];
            //System.out.println(f.length());
            InputStream in = null;
            try {
                in = new FileInputStream(f);
                in.read(raw);
            } catch (Exception e) {
                e.printStackTrace();
            }
            try {
                if (in != null)
                    in.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return defineClass(null, raw, 0, raw.length);
        }
    }
}

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.Method;
import java.net.URI;
import java.util.Arrays;
 
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.ToolProvider;
 
public class CompileSourceInMemory {
    public static void main(String args[]) throws IOException {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
 
        StringWriter writer = new StringWriter();
        PrintWriter out = new PrintWriter(writer);
        out.println("public class HelloWorld {");
        out.println("  public static void main(String args[]) {");
        out.println("    System.out.println(\"This is in another java file\");");
        out.println("  }");
        out.println("}");
        out.flush();
        out.close();
        JavaFileObject file = new JavaSourceFromString("HelloWorld", writer.toString());
        System.out.println(file);
 
        Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file);
        CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);
 
        boolean success = task.call();
        for (Diagnostic<?> diagnostic : diagnostics.getDiagnostics())
            System.out.println(diagnostic);
        System.out.println("Success: " + success);
 
        if (success) {
            try {
                MyClassLoader loader = new MyClassLoader();
 
                Class my = loader.getClassFromFile(new File("HelloWorld.class"));
 
                Method m = my.getMethod("main", new Class[] { String[].class });
 
                Object o = my.newInstance();
                m.invoke(o, new Object[] { new String[0] });
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
 
    static class JavaSourceFromString extends SimpleJavaFileObject {
        final String code;
 
        JavaSourceFromString(String name, String code) {
            super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
            this.code = code;
        }
 
        @Override
        public CharSequence getCharContent(boolean ignoreEncodingErrors) {
            return code;
        }
    }
 
    static class MyClassLoader extends ClassLoader {
 
        public Class getClassFromFile(File f) {
            byte[] raw = new byte[(int) f.length()];
            System.out.println(f.length());
            InputStream in = null;
            try {
                in = new FileInputStream(f);
                in.read(raw);
            } catch (Exception e) {
                e.printStackTrace();
            }
            try {
                if (in != null)
                    in.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return defineClass(null, raw, 0, raw.length);
        }
    }
}