Monitor proxyMonitor = (Monitor) Proxy.newProxyInstance(MonitorProxyTest.class.getClassLoader()
                , new Class[]{Monitor.class}
                , new LogMonitor(new LMonitor()));
String result = proxyMonitor.display();
assertThat("start display", is(result));

// public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)


public interface Monitor {
    public String display();
}

public class LMonitor implements Monitor {
    @Override
    public String display() {
        return "display";
    }
}

public class LogMonitor implements InvocationHandler {

    private final Monitor monitor;

    public LogMonitor(Monitor monitor) {
        this.monitor = monitor;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Object ret = method.invoke(monitor, args);
        return "start " + ret;
    }
}