1. 重写对象的equals

以ShopItem为例

public class ShopItem {

    private String name;
    private double price;

    public ShopItem(String name, double price) {
        this.name = name;
        this.price = price;
    }
}

ShopItem由两个成员变量name和price组成，

以equals方法为例
注:

1. 基本数据类型，使用其包装类比较
2. 对象使用Objects.equals比较

  @Override
    public boolean equals(Object other) {
        if (this == other) return true;
        if (other == null || getClass() != other.getClass()) return false;
        ShopItem shopItem = (ShopItem) other;
        return Double.compare(shopItem.price, price) == 0 &&
                Objects.equals(name, shopItem.name);
    }

2. 重写hashcode方法

使用 Objects.hash方法计算hash值
注意:

 @Override
    public int hashCode() {
        return Objects.hash(name, price);
    }

hashcode的算法有很多总，jdk中采用的算法是如下

   public static int hashCode(Object a[]) {
        if (a == null)
            return 0;

        int result = 1;

        for (Object element : a)
            result = 31 * result + (element == null ? 0 : element.hashCode());

        return result;
    }

2.插入删除等算法

2.0 扩容

  public void resize() {
        if (count+1 >= shoppingItems.length) {
            ShoppingItem[] tempShoppingItems = new ShoppingItem[shoppingItems.length * 2];
            for (int i = 0; i < count; i++) {
                tempShoppingItems[i] = shoppingItems[i];
            }
            shoppingItems = tempShoppingItems;
        }
    }

2.1 插入

    public void insert(ShoppingItem item, int index) {
        if (index < 0 || index >= size()) {
            return;
        }
        resize();
        for (int i = size() - 1; i >= index; i--) {
            shoppingItems[i + 1] = shoppingItems[i];
        }
        shoppingItems[index] = item;
        count++;
    }

    public void append(ShoppingItem item) {
        insert(item, (size()-1));
    }

    public void prepend(ShoppingItem item) {
        insert(item, 0);
    }

2.3删除

    public ShoppingItem deleteItemAt(int index) {
        if (index < 0 || index >= size()) {
            return null;
        } else {
            ShoppingItem deleteShoppingItem = get(index);
            for (int i = index; i < size() - 1; i++) {
                shoppingItems[i] = shoppingItems[i + 1];
            }
            shoppingItems[size() - 1] = null;
            count--;
            return deleteShoppingItem;
        }
    }

    public ShoppingItem deleteItem(String name) {
        for (int i = 0; i < size() - 1; i++) {
            ShoppingItem shoppingItem = shoppingItems[i];
            if (Objects.equals(name, shoppingItem.getName())) {
                return deleteItemAt(i);
            }
        }
        return null;
    }