package ex11_01;
/**This is a generic container class to store a list of objects
 * 
 * @author WangDong
 *@version 19th December 2011
 */

public class ObjectList {
    private Object[] list;     //之前并未写过Object类，后面别的类继承竟然可以直接用
    private int total;
    
    /**Constructor intitialises an empty list
     * @param sizeIn Used to set the maximum size of the list
     */
    public ObjectList(int sizeIn){
        list=new Object[sizeIn];
        total=0;
    }
    
    /**Add an object to the end of the list
     * @param objectIn The object to add
     * @return Returns true if the object was added successfuly
     * add false otherwise
     */
    public boolean add(Object objectIn){
        if(!isFull()){
            list[total]=objectIn;
            total++;
            return true;
        }
        else{
            return false;
        }
    }
    
    /**Reports on whether or not the list is empty
     * @return Returns true if the list is empty
     * and false otherwise
     */
    public boolean isEmpty(){
        if(total==0){
            return true;
        }
        else{
            return false;
        }
    }
    
    /**Reports on whether or not the list is full
     * @return Returns true if the list is full
     * and false otherwise
     */
    public boolean isFull(){
        if(total==list.length){
            return true;
        }
        else{
            return false;
        }
    }
    
    /**Reads an object from a specified position in the list
     * @param i The position of the object in the list
     * @return Returns the object at the specified position in the list
     * or null if no object is at at that position
     */
    public Object getItem(int positionIn){
        if(positionIn<1||positionIn>total){
            return null;
        }
        else{
            return list[positionIn-1];
        }
    }
    
    /**Reads the number of objects stored in the list*/
    public int getTotal(){
        return total;
    }
    
    /**Remove an object from the specified position in the list
     * @param numberIn The position of the object to be removed
     * @return Returns true of the item is removed successfully
     * and false otherwise
     */
    public boolean remove(int numberIn){
        if(numberIn>=1&&numberIn<=total){
            for(int i=numberIn-1;i<=total-2;i++){
                list[i]=list[i+1];
            }
            total--;
            return true;
        }
        else{
            return false;
        }
    }
    
}

package ex11_01;
/**Collection class to hold a list of Payment objects
 * 
 * @author WangDong
 *@version 19th December 2011
 */

public class PaymentList extends ObjectList{       
    /**Constructor initialises the empty list and sets the maximum list size
     */
    public PaymentList(int sizeIn){
        super(sizeIn);   //Call ObjectList constructor
    }
    
    /**Reads the payment at the given position in the list
     * @param positionIn The position of the payment in the list
     * @return Returns the payment at the position 
     */
    public Payment getPayment(int positionIn){
        if(positionIn<1||positionIn>getTotal()){
            //No object found at given position
            return null;
        }
        else{
            //Call inherited method and type cast
            return (Payment)super.getItem(positionIn);  //这里直接强制转换一下就可以吗
        }
    }
    
    /**Returns the total value of payments recorded*/
    public double calculateTotalPaid(){
        double totalPaid=0;//Intialize total paid
        //Loop throuth all payments
        for(int i=1;i<=super.getTotal();i++){
            totalPaid+=getPayment(i).getAmount();
        }
        return totalPaid;
    }
}