Java抽象类与接口区别详解

public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {
  // abstract method
  abstract void service(ServletRequest req, ServletResponse res);
 
  void init() {
    // Its implementation
  }
  // other method related to Servlet
}

public class HttpServlet extends GenericServlet {
  void service(ServletRequest req, ServletResponse res) {
    // implementation
  }
 
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
    // Implementation
  }
 
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
    // Implementation
  }
 
  // some other methods related to HttpServlet
}

public interface Externalizable extends Serializable {
  void writeExternal(ObjectOutput out) throws IOException;
 
  void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
}

public class Employee implements Externalizable {
 
  int employeeId;
  String employeeName;
 
  @Override
  public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    employeeId = in.readInt();
    employeeName = (String) in.readObject();
 
  }
  @Override
  public void writeExternal(ObjectOutput out) throws IOException {
 
    out.writeInt(employeeId);
    out.writeObject(employeeName);
  }
}