If someone wants to use the OpenGL ES 2.0 extension "GL_OES_vertex_array_object", the macro "GL_GLEXT_PROTOTYPES" must be defined in his program first. Then he can get the extension program location by calling the API eglGetProcAddress. Here is an example to use this extension.
#define GL_GLEXT_PROTOTYPES
PFNGLGENVERTEXARRAYSOESPROC glGenVertexArraysOESv;
PFNGLBINDVERTEXARRAYOESPROC glBindVertexArrayOESv;
PFNGLDELETEVERTEXARRAYSOESPROC glDeleteVertexArraysOESv;
glGenVertexArraysOESv = (PFNGLGENVERTEXARRAYSOESPROC)eglGetProcAddress ( "glGenVertexArraysOES" );
glBindVertexArrayOESv = (PFNGLBINDVERTEXARRAYOESPROC)eglGetProcAddress ( "glBindVertexArrayOES" );
glDeleteVertexArraysOESv = (PFNGLDELETEVERTEXARRAYSOESPROC)eglGetProcAddress ( "glDeleteVertexArraysOES" );
After these steps, the new alias glGenVertexArraysOESv, glBindVertexArrayOESv, glDeleteVertexArraysOESv can be use to call the VAO operation function in OpenGL ES 2.0 extensions.