如何比较 ArrayList 中的对象属性? [英] How to compare Objects attributes in an ArrayList?

问题描述

我对 Java 还很陌生，我已经用尽了我当前的所有资源来寻找答案.我想知道是否可以访问 Objects first 属性以查看它是否与特定整数匹配?

I am fairly new to Java and I have exhausted all of my current resources to find an answer. I am wondering if it possible to access an Objects first property to see if it matches a particular integer?

例如，我试图通过搜索产品 ID 来获取数据库中的产品.因此，如果我创建两个产品，例如 Product ipad = new Product(12345, "iPad", 125.0, DeptCode.COMPUTER); 和 Product ipod = new Product(12356, "iPod", 125.0, DeptCode.ELECTRONICS);(我在下面包含了这个 Product 类)，并将它们添加到一个 Arraylist，例如 Listproducts = new ArrayList<Product>(); 我怎样才能遍历这个 ArrayList 以便通过它的 ID 找到那个产品?这是我正在研究的方法:

For example, I am trying to obtain a Product that is within my Database by searching for it by it's Product ID. Therefore, if I create two products such as, Product ipad = new Product(12345, "iPad", 125.0, DeptCode.COMPUTER); and Product ipod = new Product(12356, "iPod", 125.0, DeptCode.ELECTRONICS); (I have included this Product class below), and add them to an Arraylist such as, List<Product> products = new ArrayList<Product>(); how can I loop through this ArrayList in order to find that product by its ID? This is the method I am working on:

List<Product> products = new ArrayList<Product>();


@Override
public Product getProduct(int productId) {
    // TODO Auto-generated method stub
    for(int i=0; i<products.size(); i++){
        //if statement would go here
        //I was trying: if (Product.getId() == productId) {
        System.out.println(products.get(i));
    }
    return null;
}`

我知道我可以在 for 循环中包含条件语句，但我不知道如何访问 Product 类中的 getId() 方法以将其与 productId 参数进行比较?

I know that I can include a conditional statement in the for loop but I cant figure out how to access the getId() method in the Product class to compare it the productId parameter?

 package productdb;

public class Product {
    private Integer id;
    private String name;
    private double price;
    private DeptCode dept;

    public Product(String name, double price, DeptCode code) {
        this(null, name, price, code);
    }

    public Product(Integer id, String name, double price, DeptCode code) {
        this.id = id;
        this.name = name;
        this.price = price;
        this.dept = code;
    }

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }

    public Integer getId() {
        return id;
    }


    public void setId(Integer id) {
        this.id = id;
    }

    public DeptCode getDept() {
        return dept;
    }

    public void setDept(DeptCode dept) {
        this.dept = dept;
    }

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

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

    @Override
    public String toString() {
        String info = String.format("Product [productId:%d,  name: %s, dept: %s, price: %.2f",
                id, name, dept, price);
        return info;
    }

}

请告诉我

推荐答案

您已经在以下语句中从 List 中获取了 Product:

You have already got the Product out of the List<Product> in the following statement:

System.out.println(products.get(i));

现在，您已经获得了 Product，现在要获取它的 id，您只需调用它的 getId() 方法:

Now, that you have got Product, now to get it's id, you can just call it's getId() method:

if (product.get(i).getId() == productId) {
    // Return this product.
}

---

我还建议您使用增强的 for 循环而不是像这样的传统循环:

---

I would also suggest you to use enhanced for-loop instead of the traditional loop like this:

for (Product product: products) {
    // Now you have the product. Just get the Id
    if (product.getId() == productId) {
        return product;
    }
}

此外，您应该将 productId 的类型从 Integer 更改为 int.那里不需要包装器类型.

Also, you should change the type of productId from Integer to int. You don't need a wrapper type there.

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