我读过关于使用比较器排序数组列表的内容，但在所有的例子中，人们都使用了compareTo，根据一些研究，它是字符串的一种方法。
我想根据自定义对象的一个属性(Date对象)对其数组列表进行排序 (getStartDay())。通常我通过item1.getStartDate().before(item2.getStartDate())比较它们，所以我想知道我是否可以写一些像这样的东西:
public class CustomComparator {
public boolean compare(Object object1, Object object2) {
return object1.getStartDate().before(object2.getStartDate());
}
}
public class RandomName {
...
Collections.sort(Database.arrayList, new CustomComparator);
...
}
当前回答
我已经尝试了很多不同的解决方案，可在互联网上，但解决方案，为我是可在下面的链接。
https://www.java67.com/2017/07/how-to-sort-arraylist-of-objects-using.html
其他回答
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
public class test {
public static class Person {
public String name;
public int id;
public Date hireDate;
public Person(String iname, int iid, Date ihireDate) {
name = iname;
id = iid;
hireDate = ihireDate;
}
public String toString() {
return name + " " + id + " " + hireDate.toString();
}
// Comparator
public static class CompId implements Comparator<Person> {
@Override
public int compare(Person arg0, Person arg1) {
return arg0.id - arg1.id;
}
}
public static class CompDate implements Comparator<Person> {
private int mod = 1;
public CompDate(boolean desc) {
if (desc) mod =-1;
}
@Override
public int compare(Person arg0, Person arg1) {
return mod*arg0.hireDate.compareTo(arg1.hireDate);
}
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
SimpleDateFormat df = new SimpleDateFormat("mm-dd-yyyy");
ArrayList<Person> people;
people = new ArrayList<Person>();
try {
people.add(new Person("Joe", 92422, df.parse("12-12-2010")));
people.add(new Person("Joef", 24122, df.parse("1-12-2010")));
people.add(new Person("Joee", 24922, df.parse("12-2-2010")));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Collections.sort(people, new Person.CompId());
System.out.println("BY ID");
for (Person p : people) {
System.out.println(p.toString());
}
Collections.sort(people, new Person.CompDate(false));
System.out.println("BY Date asc");
for (Person p : people) {
System.out.println(p.toString());
}
Collections.sort(people, new Person.CompDate(true));
System.out.println("BY Date desc");
for (Person p : people) {
System.out.println(p.toString());
}
}
}
具有自然排序顺序的类(例如类Number)应该实现Comparable接口，而没有自然排序顺序的类(例如类Chair)应该提供Comparator(或匿名Comparator类)。
两个例子:
public class Number implements Comparable<Number> {
private int value;
public Number(int value) { this.value = value; }
public int compareTo(Number anotherInstance) {
return this.value - anotherInstance.value;
}
}
public class Chair {
private int weight;
private int height;
public Chair(int weight, int height) {
this.weight = weight;
this.height = height;
}
/* Omitting getters and setters */
}
class ChairWeightComparator implements Comparator<Chair> {
public int compare(Chair chair1, Chair chair2) {
return chair1.getWeight() - chair2.getWeight();
}
}
class ChairHeightComparator implements Comparator<Chair> {
public int compare(Chair chair1, Chair chair2) {
return chair1.getHeight() - chair2.getHeight();
}
}
用法:
List<Number> numbers = new ArrayList<Number>();
...
Collections.sort(numbers);
List<Chair> chairs = new ArrayList<Chair>();
// Sort by weight:
Collections.sort(chairs, new ChairWeightComparator());
// Sort by height:
Collections.sort(chairs, new ChairHeightComparator());
// You can also create anonymous comparators;
// Sort by color:
Collections.sort(chairs, new Comparator<Chair>() {
public int compare(Chair chair1, Chair chair2) {
...
}
});
使用这个库，您可以对自定义对象列表进行多列排序。该库使用8.0版本的特性。样品也可在那里。这里有一个要做的示例
SortKeys sortKeys = new SortKeys();
sortKeys.addField("firstName")
.addField("age", true); // This (true) will sort the age descending
// Other ways to specify a property to the sorter are
// .addField("lastName", String.class);
// .addField("dob", Date.class, true);
// Instantiate a ListSorter
ListSorter listSorter = new ListSorter();
// Pass the data to sort (listToSort) and the "by keys" to sort (sortKeys)
List sortedList = (List<Person>) listSorter.sortList(listToSort, sortKeys);
函数和方法参考
的集合。sort方法可以使用传入的比较器对列表进行排序。该比较器可以使用Comparator. comparison方法实现，其中可以传递一个方法引用作为必要的函数。幸运的是，实际代码比这个描述简单得多。
对于Java 8:
Collections.sort(list, comparing(ClassName::getName));
or
Collections.sort(list, comparing(ClassName::getName).reversed());
另一种方法是
Collections.sort(list, comparing(ClassName::getName, Comparator.nullsLast(Comparator.naturalOrder())));
你的customComparator类必须实现java.util.Comparator才能被使用。 它还必须覆盖compare() AND equals()
compare()必须回答这个问题:对象1是否小于、等于或大于对象2?
完整文档:http://java.sun.com/j2se/1.5.0/docs/api/java/util/Comparator.html
