使用自定义排序顺序对对象的 ArrayList 进行排序 [英] Sorting an ArrayList of objects using a custom sorting order

问题描述

我希望为我的地址簿应用程序实现排序功能.

I am looking to implement a sort feature for my address book application.

我想对 ArrayList 进行排序联系数组.Contact 是一个包含四个字段的类:姓名、家庭号码、手机号码和地址.我想按 name 排序.

I want to sort an ArrayList<Contact> contactArray. Contact is a class which contains four fields: name, home number, mobile number and address. I want to sort on name.

如何编写自定义排序函数来执行此操作?

How can I write a custom sort function to do this?

推荐答案

这是一个关于排序对象的教程:

Here's a tutorial about ordering objects:

• Java 教程 - 集合 - 对象排序

虽然我会举一些例子，但我还是建议你阅读它.

Although I will give some examples, I would recommend to read it anyway.

有多种方法可以对 ArrayList 进行排序.如果你想定义一个自然(默认)排序，那么你需要让Contact实现Comparable.假设您希望默认对 name 进行排序，然后执行(为简单起见省略了空检查):

There are various way to sort an ArrayList. If you want to define a natural (default) ordering, then you need to let Contact implement Comparable. Assuming that you want to sort by default on name, then do (nullchecks omitted for simplicity):

public class Contact implements Comparable<Contact> {

    private String name;
    private String phone;
    private Address address;

    @Override
    public int compareTo(Contact other) {
        return name.compareTo(other.name);
    }

    // Add/generate getters/setters and other boilerplate.
}

这样你就可以做

List<Contact> contacts = new ArrayList<Contact>();
// Fill it.

Collections.sort(contacts);

---

如果要定义外部可控排序(覆盖自然排序)，则需要创建一个Comparator:

---

If you want to define an external controllable ordering (which overrides the natural ordering), then you need to create a Comparator:

List<Contact> contacts = new ArrayList<Contact>();
// Fill it.

// Now sort by address instead of name (default).
Collections.sort(contacts, new Comparator<Contact>() {
    public int compare(Contact one, Contact other) {
        return one.getAddress().compareTo(other.getAddress());
    }
}); 

---

您甚至可以在 Contact 本身中定义 Comparator 以便您可以重用它们而不是每次都重新创建它们:

---

You can even define the Comparators in the Contact itself so that you can reuse them instead of recreating them everytime:

public class Contact {

    private String name;
    private String phone;
    private Address address;

    // ...

    public static Comparator<Contact> COMPARE_BY_PHONE = new Comparator<Contact>() {
        public int compare(Contact one, Contact other) {
            return one.phone.compareTo(other.phone);
        }
    };

    public static Comparator<Contact> COMPARE_BY_ADDRESS = new Comparator<Contact>() {
        public int compare(Contact one, Contact other) {
            return one.address.compareTo(other.address);
        }
    };

}

可以如下使用:

List<Contact> contacts = new ArrayList<Contact>();
// Fill it.

// Sort by address.
Collections.sort(contacts, Contact.COMPARE_BY_ADDRESS);

// Sort later by phone.
Collections.sort(contacts, Contact.COMPARE_BY_PHONE);

---

为了使顶部更加完美，您可以考虑使用通用 javabean 比较器:

public class BeanComparator implements Comparator<Object> {

    private String getter;

    public BeanComparator(String field) {
        this.getter = "get" + field.substring(0, 1).toUpperCase() + field.substring(1);
    }

    public int compare(Object o1, Object o2) {
        try {
            if (o1 != null && o2 != null) {
                o1 = o1.getClass().getMethod(getter, new Class[0]).invoke(o1, new Object[0]);
                o2 = o2.getClass().getMethod(getter, new Class[0]).invoke(o2, new Object[0]);
            }
        } catch (Exception e) {
            // If this exception occurs, then it is usually a fault of the developer.
            throw new RuntimeException("Cannot compare " + o1 + " with " + o2 + " on " + getter, e);
        }

        return (o1 == null) ? -1 : ((o2 == null) ? 1 : ((Comparable<Object>) o1).compareTo(o2));
    }

}

您可以按如下方式使用:

which you can use as follows:

// Sort on "phone" field of the Contact bean.
Collections.sort(contacts, new BeanComparator("phone"));

(如您在代码中看到的，可能已经覆盖了空字段以避免排序期间出现 NPE)

这篇关于使用自定义排序顺序对对象的 ArrayList 进行排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！