EECS1030Z Test 3

Thursday February 26, 2015, 14:30-15:45
Lab 01
Version H

Programming question

Implement the USBPort class having the API shown here. A skeleton can be found here.

• You have to put your USBPort class in the test3 package.
• USBPort must be a multiton.
• You should not add any public features to the class.
• You must add an appropriate static field to implement the multiton.
• You must implement the private constructor found in the skeleton code even though it does not appear in the API.
• You may override toString if you want to help with testing.

package test3;
import java.util.HashMap;
import java.util.Map;


/**
 * A class that represents USB ports on a computer. Each USB port
 * has a unique integer port number, and it is guaranteed that there
 * is only one USBPort for each port number. Each USB port is either connected
 * or not connected to an external device of some kind (such as a
 * USB key, for example).
 * 
 * @author EECS1030_2014_14W
 *
 */
public class USBPort {
  private static Map<Integer, USBPort> instances = new HashMap<Integer, USBPort>();
  
  private int portNumber;
  private boolean isConnected;
  
  /**
   * Create a new USB port having the given port number. The USB port
   * is not allowed to be connected to an external device when it is
   * created.
   * 
   * @param portNumber the port number of the USB port
   * @pre. portNumber >= 0
   * @pre. the USB port is not connected to an external device
   */
  private USBPort(int portNumber) {
    this.portNumber = portNumber;
    this.isConnected = false;
  }
  
  /**
   * Return the port number of this USB port.
   * 
   * @return the port number of this USB port
   */
  public int getPortNumber() {
    return this.portNumber;
  }
  
  /**
   * Connect the port to an external device. The state of the port
   * does not change if the port is already connected to an external
   * device. 
   */
  public void connect() {
    this.isConnected = true;
  }
  
  /**
   * Disconnect the port from the external device. The state of the port
   * does not change if the port is already disconnected. 
   */
  public void disconnect() {
    this.isConnected = false;
  }
  
  /**
   * Returns <code>true</code> if the port is connected to an external
   * device, and <code>false</code> otherwise.
   * 
   * @return <code>true</code> if the port is connected to an external
   * device, and <code>false</code> otherwise.
   */
  public boolean hasConnection() {
    return this.isConnected;
  }
  
  /**
   * Get the USB port with the given port number. The port number must
   * be an integer value greater than zero. A new USB port is created if
   * a USB port with the given port number does not exist. If a new USB
   * port is created then it is created assuming that the port is not
   * connected to an external device.
   * 
   * @param portNumber the port number of the desired USB port
   * @return a USB port with the desired port number
   * @throws IllegalArgumentException if the port number is less
   * than or equal to zero
   */
  public static USBPort getPort(int portNumber) {
    if (portNumber <= 0) {
      throw new IllegalArgumentException();
    }
    USBPort p = USBPort.instances.get(portNumber);
    if (p == null) {
      p = new USBPort(portNumber);
      USBPort.instances.put(portNumber, p);
    }
    return p;
  }
  
  /**
   * Returns the number of USB ports that have been created.
   * 
   * @return the number of USB ports that have been created
   */
  public static int getNumberOfPorts() {
    return USBPort.instances.size();
  }
  
  

}

Other questions

public static void main(String[] args) {
  USBPort u = USBPort.getPort(1);
  USBPort v = USBPort.getPort(2);
  USBPort w = USBPort.getPort(3);
  USBPort x = USBPort.getPort(1);
  
  // remainder of main not shown
}

Question 3

What is the name of the relationship between the two classes shown in the following UML diagram:

Type your answer here: aggregation