问buffer.flip()方法的确切功能是什么？

EN

        ByteBuffer buffer = ByteBuffer.allocate(100);
        byte[] outputBytes = "Hello World!".getBytes();
        buffer.put(outputBytes);
        long int1Pos = outputBytes.length;
        buffer.putInt(245);

        binChannel.write(buffer);

        java.io.RandomAccessFile ra = new java.io.RandomAccessFile("data.dat", "rwd");
        FileChannel channel = ra.getChannel();

        ByteBuffer readBuffer = ByteBuffer.allocate(100);

        channel.position(int1Pos);
        channel.read(readBuffer);
        readBuffer.flip();
        System.out.println("Int3 = " + readBuffer.getInt());
         } catch(IOException e){
         }