Array with class base type

[thebluestar]

ShoppingListItem.java

package problem2class;

public class ShoppingListItem {

    private String name;
    private int numOfItems;
    private double price;

    public ShoppingListItem(String name, int quantity, double pricePerUnit) {
        this.name = name;
        numOfItems = quantity;
        price = pricePerUnit;

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getNumOfItems() {
        return numOfItems;
    }

    public void setNumOfItems(int numOfItems) {
        this.numOfItems = numOfItems;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public double getCost() {
        return numOfItems * price;
    }

    public void setQuantity(int quantity) {
        numOfItems = quantity;
    }
    public static void main(String[] linh) {
        ShoppingListItem I1;
        I1 = new ShoppingListItem("Kenturky",12,1200);
        System.out.println("Now show the content of the Item:");
        System.out.println("Name is:"+I1.getName() + " Price for each item:"+I1.getPrice() +" Num of items:"+I1.getNumOfItems());
        System.out.println("So the cost is: "+I1.getCost());
    }
}

ShoppingList.java

package problem2class;
public class ShoppingList {
    public static ShoppingListItem[] items = new ShoppingListItem[10];
  //  public static int index=0;
    public static double totalCost=0;
    static ShoppingListItem I1 = new ShoppingListItem("milk",1,23);
  //  static ShoppingListItem I2 = new ShoppingListItem("cofee",12,30);
    public ShoppingList() {

    }
    public void add(ShoppingListItem i) {
        items[0] = new ShoppingListItem(i.getName(),i.getNumOfItems(),i.getCost());
        //index++;
        System.out.println("adding done!");
    }
    public double getTotalCost() {
        //double totalCost =0;
        int i;
        int len = items.length;
        System.out.println("length is"+len);
        for (i = 0; i < items.length; i++) {
            totalCost =totalCost + items[i].getCost();
            System.out.println("each"+items[i].getCost());
        }
        return totalCost;
    }
    public static void main(String[] args) {
       ShoppingList L1 = new ShoppingList();
        L1.add(I1);
        System.out.println("Total cost is" + L1.getTotalCost());
    }
}

In the above exercise I add the items into the list then compute the totalCost of items stored in the list.
But it does not work properly.
Please help me solve this.
Thanks a lot!

[LReynolds]

I just briefly glanced over it, but two things I notice initially are:
you only need one main method. Leave the main method in ShoppingList and it creates an instance of ShoppingListItem but delete it out of ShoppingListItem.

Second problem: Since you are only adding one item to the shoppingList right now it doesnt matter, but if you add more than one it will overwrite previously entered ones. in your add method, you are adding it to the item[] at 0. So when you add another one it will add it to the same spot and overwrite the old one.

anyway, let us know what kind of errors you are getting as well.

ShoppingListItem.java

package problem2class;

public class ShoppingListItem {

    private String name;
    private int numOfItems;
    private double price;

    public ShoppingListItem(String name, int quantity, double pricePerUnit) {
        this.name = name;
        numOfItems = quantity;
        price = pricePerUnit;

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getNumOfItems() {
        return numOfItems;
    }

    public void setNumOfItems(int numOfItems) {
        this.numOfItems = numOfItems;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public double getCost() {
        return numOfItems * price;
    }

    public void setQuantity(int quantity) {
        numOfItems = quantity;
    }
    public static void main(String[] linh) {
        ShoppingListItem I1;
        I1 = new ShoppingListItem("Kenturky",12,1200);
        System.out.println("Now show the content of the Item:");
        System.out.println("Name is:"+I1.getName() + " Price for each item:"+I1.getPrice() +" Num of items:"+I1.getNumOfItems());
        System.out.println("So the cost is: "+I1.getCost());
    }
}

ShoppingList.java

package problem2class;
public class ShoppingList {
    public static ShoppingListItem[] items = new ShoppingListItem[10];
  //  public static int index=0;
    public static double totalCost=0;
    static ShoppingListItem I1 = new ShoppingListItem("milk",1,23);
  //  static ShoppingListItem I2 = new ShoppingListItem("cofee",12,30);
    public ShoppingList() {

    }
    public void add(ShoppingListItem i) {
        items[0] = new ShoppingListItem(i.getName(),i.getNumOfItems(),i.getCost());
        //index++;
        System.out.println("adding done!");
    }
    public double getTotalCost() {
        //double totalCost =0;
        int i;
        int len = items.length;
        System.out.println("length is"+len);
        for (i = 0; i < items.length; i++) {
            totalCost =totalCost + items[i].getCost();
            System.out.println("each"+items[i].getCost());
        }
        return totalCost;
    }
    public static void main(String[] args) {
       ShoppingList L1 = new ShoppingList();
        L1.add(I1);
        System.out.println("Total cost is" + L1.getTotalCost());
    }
}

In the above exercise I add the items into the list then compute the totalCost of items stored in the list.
But it does not work properly.
Please help me solve this.
Thanks a lot!

[thebluestar]

package problem2class;

public class ShoppingListItem {

    private String name;
    private int numOfItems;
    private double price;

    public ShoppingListItem(String name, int quantity, double pricePerUnit) {
        this.name = name;
        numOfItems = quantity;
        price = pricePerUnit;

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getNumOfItems() {
        return numOfItems;
    }

    public void setNumOfItems(int numOfItems) {
        this.numOfItems = numOfItems;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public double getCost() {
        return numOfItems * price;
    }

    public void setQuantity(int quantity) {
        numOfItems = quantity;
    }
 
}

package problem2class;

public class ShoppingList {

    public static ShoppingListItem[] items = new ShoppingListItem[10];
    public static int index = 0;
 //   public static double totalCost;
    static ShoppingListItem I1 = new ShoppingListItem("milk", 2, 20);
    static ShoppingListItem I2 = new ShoppingListItem("cofee", 12, 2);

    public ShoppingList() {
    }

    public void add(ShoppingListItem i) {
        System.out.println("index is " + index);
        items[index] = new ShoppingListItem(i.getName(), i.getNumOfItems(), i.getPrice());
        System.out.println("adding done!" + items[index].getName() + "price" + items[index].getCost());
        index++;
    }

    public double getTotalCost() {
        double totalCost =0;
        int i;
        int len = items.length;
        System.out.println("length is" + len);
        for (i = 0; i < items.length; i++) {
            totalCost = totalCost + items[i].getCost();
            System.out.println("each" + items[i].getCost());
            System.out.println("totalCost" +totalCost);
        }
        return totalCost;
    }

    public static void main(String[] args) {
        ShoppingList L1 = new ShoppingList();
        L1.add(I1);
        L1.add(I2);
        System.out.println("Total cost is" + L1.getTotalCost());
    }
}

I mean the getTotalCost() in the shoppingList does not work, I don't know why.
Firstly, I have just try adding 1 item.
Also, I put a main into the class shoppingListItem just for checking.
I changed something so you can see my idea clearly.

[thebluestar]

I have already fixed this problem

public double getTotalCost() {
        double totalCost =0;
        int i;
        int len = items.length;
        System.out.println("length is" + len);
        for (i = 0; i < index; i++) {
            totalCost = totalCost + items[i].getCost();
        }
        return totalCost;
    }