ruby dk.rb init
ruby dk.rb install

jekyll build
jekyll build --watch
jekyll build -w
jekyll serve
jekyll serve --watch
jekyll serve -w

ERROR: Could not find a valid gem 'jekyll' (>= 0), here is why:
Unable to download data from https://rubygems.org/ - 
Errno::ETIMEDOUT: Operation timed out - connect(2) (https://rubygems.org/latest_specs.4.8.gz)

$ gem sources --remove https://rubygems.org/
$ gem sources -a http://ruby.taobao.org/
$ gem sources -l
*** CURRENT SOURCES ***
http://ruby.taobao.org  
$ gem install jekyll

ByteOrder bOrder = vertexData.order();
if (bOrder == ByteOrder.BIG_ENDIAN) {
    // is big endian
} else {
    // ByteOrder.LITTLE_ENDIAN
}

// use native order
byteBuffer.order(ByteOrder.nativeOrder())

float[] tableVerticesWithTriangles = {
    // first triangle.
    -0.5f, -0.5f, 0.5f, 0.5f, -0.5f, 0.5f,

    // second triangle.
    -0.5f, -0.5f, 0.5f, -0.5f, 0.5f, 0.5f,

    // middle line
    -0.5f, 0f, 0.5f, 0f,

    // two points
    0f, -0.25f, 0f, 0.25f 
};
FloatBuffer vertexData = ByteBuffer.allocate(tableVerticesWithTriangles.length * BYTES_PER_FLOAT).order(ByteOrder.nativeOrder()).asFloatBuffer();
// ... when pass the vertexData to OpenGL memory:
vertexData.position(0);
// crash here: "java.lang.IllegalArgumentException: Must use a native order direct Buffer"
glVertexAttribPointer(aPostionLocation, POSITION_COMPONENT_COUNT, GL_FLOAT, false, 0, vertexData); 

// this is ok. use allocateDirect. 
// The vertBuff buffer needs to be direct so that it isn't moved around in memory. [from StackOverflow](http://stackoverflow.com/questions/11012669/opengl-es-rendereing-error)
// You need to use the allocateDirect(int) method from the ByteBuffer class.
vertexData = ByteBuffer.allocateDirect(tableVerticesWithTriangles.length * BYTES_PER_FLOAT).order(ByteOrder.nativeOrder()).asFloatBuffer();