假设你有一些对象，它们有几个字段可以比较:
public class Person {
private String firstName;
private String lastName;
private String age;
/* Constructors */
/* Methods */
}
所以在这个例子中，当你问if:
a.compareTo(b) > 0
你可能会问a的姓是不是在b的姓之前，或者a的年龄是不是比b大，等等……
在不增加不必要的混乱或开销的情况下，在这些类型的对象之间进行多重比较的最干净的方法是什么?
comparable接口只允许通过一个字段进行比较 在我看来，添加大量的比较方法(如compareByFirstName()， compareByAge()等)是混乱的。
那么最好的解决办法是什么呢?
当前回答
晚做总比不到好——如果你正在寻找不必要的混乱或开销，那么很难同时在最少的代码/快速执行方面击败下面的方法。
数据类:
public class MyData {
int id;
boolean relevant;
String name;
float value;
}
比较器:
public class MultiFieldComparator implements Comparator<MyData> {
@Override
public int compare(MyData dataA, MyData dataB) {
int result;
if((result = Integer.compare(dataA.id, dataB.id)) == 0 &&
(result = Boolean.compare(dataA.relevant, dataB.relevant)) == 0 &&
(result = dataA.name.compareTo(dataB.name)) == 0)
result = Float.compare(dataA.value, dataB.value);
return result;
}
}
如果你只是想按自定义顺序对集合进行排序，那么下面的代码就更清晰了:
myDataList.sort((dataA, dataB) -> {
int result;
if((result = Integer.compare(dataA.id, dataB.id)) == 0 &&
(result = Boolean.compare(dataA.relevant, dataB.relevant)) == 0 &&
(result = dataA.name.compareTo(dataB.name)) == 0)
result = Float.compare(dataA.value, dataB.value);
return result;
});
其他回答
如果用户有多种方式对人排序，你也可以在某个地方设置多个comparator常量。大多数排序操作和排序集合都以比较器作为参数。
您可以实现一个Comparator来比较两个Person对象，并且可以检查任意数量的字段。你可以在比较器中放入一个变量，告诉它与哪个字段进行比较，尽管只编写多个比较器可能会更简单。
//Following is the example in jdk 1.8
package com;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
class User {
private String firstName;
private String lastName;
private Integer age;
public Integer getAge() {
return age;
}
public User setAge(Integer age) {
this.age = age;
return this;
}
public String getFirstName() {
return firstName;
}
public User setFirstName(String firstName) {
this.firstName = firstName;
return this;
}
public String getLastName() {
return lastName;
}
public User setLastName(String lastName) {
this.lastName = lastName;
return this;
}
}
public class MultiFieldsComparision {
public static void main(String[] args) {
List<User> users = new ArrayList<User>();
User u1 = new User().setFirstName("Pawan").setLastName("Singh").setAge(38);
User u2 = new User().setFirstName("Pawan").setLastName("Payal").setAge(37);
User u3 = new User().setFirstName("Anuj").setLastName("Kumar").setAge(60);
User u4 = new User().setFirstName("Anuj").setLastName("Kumar").setAge(43);
User u5 = new User().setFirstName("Pawan").setLastName("Chamoli").setAge(44);
User u6 = new User().setFirstName("Pawan").setLastName("Singh").setAge(5);
users.add(u1);
users.add(u2);
users.add(u3);
users.add(u4);
users.add(u5);
users.add(u6);
System.out.println("****** Before Sorting ******");
users.forEach(user -> {
System.out.println(user.getFirstName() + " , " + user.getLastName() + " , " + user.getAge());
});
System.out.println("****** Aftre Sorting ******");
users.sort(
Comparator.comparing(User::getFirstName).thenComparing(User::getLastName).thenComparing(User::getAge));
users.forEach(user -> {
System.out.println(user.getFirstName() + " , " + user.getLastName() + " , " + user.getAge());
});
}
}
你也可以看看实现Comparator的Enum。
http://tobega.blogspot.com/2008/05/beautiful-enums.html
e.g.
Collections.sort(myChildren, Child.Order.ByAge.descending());
//here threshold,buyRange,targetPercentage are three keys on that i have sorted my arraylist
final Comparator<BasicDBObject>
sortOrder = new Comparator<BasicDBObject>() {
public int compare(BasicDBObject e1, BasicDBObject e2) {
int threshold = new Double(e1.getDouble("threshold"))
.compareTo(new Double(e2.getDouble("threshold")));
if (threshold != 0)
return threshold;
int buyRange = new Double(e1.getDouble("buyRange"))
.compareTo(new Double(e2.getDouble("buyRange")));
if (buyRange != 0)
return buyRange;
return (new Double(e1.getDouble("targetPercentage")) < new Double(
e2.getDouble("targetPercentage")) ? -1 : (new Double(
e1.getDouble("targetPercentage")) == new Double(
e2.getDouble("targetPercentage")) ? 0 : 1));
}
};
Collections.sort(objectList, sortOrder);
