这是一个关于订购对象的教程：

虽然我会给出一些例子,但我仍然建议你阅读它.

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,那么你需要让联系人实现Comparable.假设你想在名称上默认排序,那么为了简单起见省略了nullchecks：

public class Contact implements Comparable {

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.

}

这样你就可以做到

List contacts = new ArrayList();

// Fill it.

Collections.sort(contacts);

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

List contacts = new ArrayList();

// Fill it.

// Now sort by address instead of name (default).

Collections.sort(contacts, new Comparator() {

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Comparators,以便您可以重复使用它们,而不是每次都重新创建它们：

public class Contact {

private String name;

private String phone;

private Address address;

// ...

public static Comparator COMPARE_BY_PHONE = new Comparator() {

public int compare(Contact one, Contact other) {

return one.phone.compareTo(other.phone);

}

};

public static Comparator COMPARE_BY_ADDRESS = new Comparator() {

public int compare(Contact one, Contact other) {

return one.address.compareTo(other.address);

}

};

}

可以使用如下：

List contacts = new ArrayList();

// Fill it.

// Sort by address.

Collections.sort(contacts, Contact.COMPARE_BY_ADDRESS);

// Sort later by phone.

Collections.sort(contacts, Contact.COMPARE_BY_PHONE);

最重要的是,您可以考虑使用通用的javabean比较器：

public class BeanComparator implements Comparator {

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) o1).compareTo(o2));

}

}

您可以使用如下：

// Sort on "phone" field of the Contact bean.

Collections.sort(contacts, new BeanComparator("phone"));

(正如您在代码中看到的那样,在排序过程中可能已经覆盖了空字段以避免NPE)