Java使用自定义排序顺序对对象的ArrayList进行排序

Java使用自定义排序顺序对对象的ArrayList进行排序

这是有关订购对象的教程：

Java教程-集合-对象排序
尽管我会举一些例子，但我还是建议你阅读它。

有多种排序方式

ArrayList

。如果要定义自然的（默认）排序，则需要让

ContactImplement

实现

Comparable

。假设你想默认在上进行排序name，然后执行（为简单起见，省略了nullchecks）：

public class Contact implements Comparable<Contact> {    private String name;    private String phone;    private Address address;    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：

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());    }}); 

你甚至可以Comparator在Contact自身中定义，以便你可以重用它们，而不必每次都重新创建它们：

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);

为了使结果更好，你可以考虑使用通用的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));    }}

你可以使用以下方法：

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

（如你在代码中所见，可能的空字段已经被覆盖以避免在排序过程中出现NPE）