code: /**
  Copyright (c) 2007-2013 Alysson Bessani, Eduardo Alchieri, Paulo Sousa, and the authors indicated in the @author tags
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
  http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  */
  package bftsmart.communication;
  
  import java.io.Externalizable;
  import java.io.IOException;
  import java.io.ObjectInput;
  import java.io.ObjectOutput;
  
  /**
   * This is the super-class for all other kinds of messages created by JBP
   * 
   */
  
  public abstract class SystemMessage implements Externalizable {
  
      protected int sender; // ID of the process which sent the message
      public transient boolean authenticated; // set to TRUE if the message was received
                                              // with a (valid) mac, FALSE if no mac was given
                                              // note that if the message arrives with an
                                              // invalid MAC, it won't be delivered
  
      /**
       * Creates a new instance of SystemMessage
       */
      public SystemMessage(){}
      
      /**
       * Creates a new instance of SystemMessage
       * @param sender ID of the process which sent the message
       */
      public SystemMessage(int sender){
          this.sender = sender;
      }
      
      /**
       * Returns the ID of the process which sent the message
       * @return
       */
      public final int getSender() {
          return sender;
      }
  
      // This methods implement the Externalizable interface
      @Override
      public void writeExternal(ObjectOutput out) throws IOException {
          out.writeInt(sender);
      }
      
      @Override
      public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
          sender = in.readInt();
      }
  }
  