Java. util. List multi-field sorting

You can useJava. util. Collections. Sort (list <t>, comparator <? Super T>)This is an easy-to-use method. However, it is often seen that someone is asking how to sort multiple fields of an element. This question is like an SQL statement'Order'Sentence, followed by several sorting conditions.

For example, for sorting element FOO:

Class Foo {

Int;

Int B;

}

Foo. A is the first sorting field, and foo. B is the second sorting field, that is, the foo. B is determined under the condition of two Foo such as Foo.. Then our comparator can perform the following operations:

Collections. sort (l, new Comparator <Foo> () {<br/> @ Override <br/> public int compare (Foo f1, Foo f2) {<br/> if (f1.a-f2.a> 0) {<br/> return 1; <br/>} else if (f1.a-f2.a <0) {<br/> return-1; <br/>} else {// Foo. a equal, then check Foo. B <br/> return f1. B-f2. B; <br/>}< br/> }});

 

Or you can use a method that is more common than others:

/** <Br/> * Sort <code> List </code> by multiple conditions. <br> <br/> * It's like SQL 'ORDER BY' clause. input multiple <code> Comparator </code> <br/> * in List as argument. <br/> * @ param <T> <br/> * @ param list <br/> * @ param comparatorList <br/> * @ throws IllegalArgumentException if comparatorList is empty <br/> * @ author shengyuan. lu Shengyuan <michaellufhl@yahoo.com.cn> <br/> */<br/> public static <T> void sort (List <T> list, final List <Comparator <T> comparatorList) {<br/> if (comparatorList. isEmpty () {// Always equals, if no Comparator. <br/> throw new IllegalArgumentException ("comparatorList is empty. "); <br/>}< br/> Comparator <T> comparator = new Comparator <T> () {<br/> public int compare (T o1, T o2) {<br/> for (Comparator <T> c: comparatorList) {<br/> if (c. compare (o1, o2)> 0) {<br/> return 1; <br/>} else if (c. compare (o1, o2) <0) {<br/> return-1; <br/>}< br/> return 0; <br/>}< br/>}; <br/> Collections. sort (list, comparator); <br/>}

The most efficient way is to combine each sorted comparator into a comparator and then sort it.