基于给定参数以Java打印arraylist的特定元素

Question

我正在处理的任务是基于Author类创建一个arraylist，它的属性是:ID、Author's name、book和Nationity。除此之外，我不得不创建另一个类，它接收ID作为参数，并返回相应的作者信息。我的问题是，代码是我写的，但无论我的输入接收到什么ID，它总是检索到同一个作者的信息。有人能帮我吗？

author.java

public class Author {
    
    private int id;
    private String name;
    private string book;
    private string country;
    
    public Author(int id, String name, String book, String country) {
        this.id = id;
        this.name = name;
        this.book = book;
        this.country = country;
    }
    
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
    
    public int getBook() {
        return book;
    }

    public int getCountry() {
        return country;
    }
    
    @Override
    public String toString() {
        return "Id: " + this.id + ", Name: " + this.name + ", Book:" + this.book + ", Country:" + this.country;
    }
}

getAuthor.java（用于根据ID检索作者信息的类）

public class GetAuthor {
    
    public Author returnAuthor(int id, ArrayList<Author> list) {
        
        Author author = null;
        id = 0;
        for (int i = 0 ; i < list.size() ; i++) {
            if(author == null || author(i).getId() == id) {
                author = list.get(i);
                id = list.get(i).getId();
            }
        }
        return author;  
    }
}

main.java

public class Main {

    public static void main(String[] args) {
             
        Author w1 = new Author(1, "Franz Kafka", " The Metamorphosis", "Austria");
        Author w2 = new Author(2, "Neil Gaiman", "Sandman", "England");
        Author w3 = new Author(3, "Jack Kerouac", "On The Road", "USA");

        ArrayList<Author> authors = new ArrayList<>();
        authors.add(w1);
        authors.add(w2);
        authors.add(w3);

        for(int i = 0 ; i < authors.size() ; i++){
            System.out.println(authors.get(i));
            }
        
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter the author's ID: ");

        int num = scan.nextInt();
        
        GetAuthor theAuthor = new GetAuthor();
        Author author = theAuthor.returnAuthor(num,authors);
        
        System.out.println(author);  
    }
}

Answer 1

        id = 0;

在这里,您将重写ID的传入值；这可能就是为什么你总是得到相同的答案。

            if(author == null || author(i).getId() == id) {

这甚至不应该编译；author不是方法（在您的示例中）。

Answer 2

公共静态作者returnAuthor（int id,ArrayList列表）{

    return list.stream().filter(auth -> auth.getId()==id).findFirst().orElse(null);
}