Why does TCP send data through byte stream and print stream? And UDP transmission is so simple?

  java, question

The first is the code of TCP’s client

//1. Create a client Socket and specify the server address and port
 Socket socket = new Socket("localhost",8888);
 //2. Obtain the output stream and send information to the server side
 OutputStream os = socket.getOutputStream();  //byte output stream
 PrintWriter pw = new PrintWriter(os);  //Wrap output stream as print stream
 Pw.write ("username: admin;  Password: 453 ");
 pw.flush();  //Refresh cache and output to server side

Then the code of the UDP client

//1. Define the address, port number and data of the server
 InetAddress address = InetAddress.getByName("localhost");
 int port=8000;
 Byte[] data = "username: admin;  Password: 123".getBytes ();
 //2. Create a datagram containing the data information sent
 DatagramPacket packet=new DatagramPacket(data,data.length,address,port);
 //3. Create DatagramSocket Object
 DatagramSocket socket =new DatagramSocket();
 //4. Send Datagram to Server

The client here sends some data to the local server. What I cannot understand is why TCP is so complicated. Get the output stream, wrap the print stream, and refresh the cache once. In contrast, UDP is so simple.
Why is this?
I think it may be a matter of agreement. It seems that the foundation has to be supplemented recently.

Because TCP is based on flow, while UDP is based on message.