class loader demo

ClassLoaderTest.java

import java.io.*;

public class ClassLoaderTest {
    public static void main(String[] args) throws Exception {
        ClassLoader myLoader = new ClassLoader() {
            @Override
            public Class<?> loadClass(String name) throws ClassNotFoundException {
                try {
                    String fileName = "foo/" + name.replace('.', '/') + ".class";
                    System.out.println(fileName);
                    InputStream is = getClass().getResourceAsStream(fileName);
                    if (is == null) {
                        System.out.println("'is' is null when loading " + fileName);
                        return super.loadClass(name);
                    }
                    byte[] b = new byte[is.available()];
                    is.read(b);
                    return defineClass(name, b, 0, b.length);
                } catch (IOException e) {
                    throw new ClassNotFoundException(name);
                }
            }
        };
        Object obj = myLoader.loadClass("pack.Main").newInstance();
        System.out.println("obj.getClass is " + obj.getClass());
        System.out.println(obj.hashCode());
    }
}

foo.pack.Main.java

package pack;

public class Main {
    /* replace filename '.' with '/' and compile it */
    public int hashCode() {
        System.out.println("in Main");
        return 1024;
    }
}