What's the diffrence between DatagramPacket.ge

问题:

In the code segment below,

DatagramPacket rPacket
rPacket  = new DatagramPacket(new byte[2000], 2000);
.. do some socket.receive ..

what would be the difference between DatagramPacket.getData().length and DatagramPacket.getLength() in java

回答1:

The difference is that the first returns the size of the array used to construct the object, which never changes; the second returns the smaller of the length supplied to the constructor and the actual length of the smallest datagram most recently received, which changes on every receive.

回答2:

From javadoc of class DataGrammPacket

getLength(): Returns the length of the data to be sent or the length of the data received.

getData(): Returns the data buffer. The data received or the data to be sent starts from the <code>offset</code> in the buffer, and runs for <code>length</code> long.

furthe you have to know the setData():

 Set the data buffer for this packet. This sets the
     * data, length and offset of the packet.
     *
     * @param buf the buffer to set for this packet
     *
     * @param offset the offset into the data
     *
     * @param length the length of the data 
     *       and/or the length of the buffer used to receive data
 setData(byte[] buf, int offset, int length)

The Constructor also calls the setData()