1. Activity的加载流程

在ActivityThread中的 performLaunchActivity()方法中调用 newActivity()方法，

Activity activity = null;
        try {
            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass())；

然后点击 newActivity()方法，进入：

public Activity newActivity(ClassLoader cl, String className,
            Intent intent)
            throws InstantiationException, IllegalAccessException,
            ClassNotFoundException {
        // 通过 ClassLoader找到 Activity的 class，然后利用反射实例化  TestActivity对象
        return (Activity)cl.loadClass(className).newInstance();
    }

也就是说我们的 Activity是通过来创建的，所有类的加载都是通过 ClassLoader.findName来找到Class来加载；

(Activity)cl.loadClass(className).newInstance();

上边的ClassLoader 就是 PathClassLoader ，继承关系：
PathClassLoader -> BaseDexClassLoader -> ClassLoader

protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
            // First, check if the class has already been loaded
            Class c = findLoadedClass(name)；
                if (c == null) {
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();
                    c = findClass(name);
                }
            }
            return c;
    }

有这段代码可知，最终调用的是findClass(name);