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
它很容易做到使用谷歌的番石榴库。
例如对象。equals (name, name2) &&对象。Equal (age, age2) &&…
更多的例子:
https://stackoverflow.com/a/5039178/1180621
其他回答
如果我们必须基于多个字段对Person对象进行排序，则相同的代码实现在这里。
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class Person {
private String firstName;
private String lastName;
private int age;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Person(String firstName, String lastName, int age) {
this.firstName = firstName;
this.lastName = lastName;
this.age = age;
}
static class PersonSortingComparator implements Comparator<Person> {
@Override
public int compare(Person person1, Person person2) {
// for first name comparison
int firstNameCompare = person1.getFirstName().compareTo(person2.getFirstName());
// for last name comparison
int lastNameCompare = person1.getLastName().compareTo(person2.getLastName());
// for last name comparison
int ageCompare = person1.getAge() - person2.getAge();
// Now comparing
if (firstNameCompare == 0) {
if (lastNameCompare == 0) {
return ageCompare;
}
return lastNameCompare;
}
return firstNameCompare;
}
}
public static void main(String[] args) {
Person person1 = new Person("Ajay", "Kumar", 27);
Person person2 = new Person("Ajay","Gupta", 23);
Person person3 = new Person("Ajay","Kumar", 22);
ArrayList<Person> persons = new ArrayList<>();
persons.add(person1);
persons.add(person2);
persons.add(person3);
System.out.println("Before Sorting:\n");
for (Person person : persons) {
System.out.println(person.firstName + " " + person.lastName + " " + person.age);
}
Collections.sort(persons, new PersonSortingComparator());
System.out.println("After Sorting:\n");
for (Person person : persons) {
System.out.println(person.firstName + " " + person.lastName + " " + person.age);
}
}
}
另一个可以考虑的选项是Apache Commons。它提供了很多选项。
import org.apache.commons.lang3.builder.CompareToBuilder;
Ex:
public int compare(Person a, Person b){
return new CompareToBuilder()
.append(a.getName(), b.getName())
.append(a.getAddress(), b.getAddress())
.toComparison();
}
import com.google.common.collect.ComparisonChain;
/**
* @author radler
* Class Description ...
*/
public class Attribute implements Comparable<Attribute> {
private String type;
private String value;
public String getType() { return type; }
public void setType(String type) { this.type = type; }
public String getValue() { return value; }
public void setValue(String value) { this.value = value; }
@Override
public String toString() {
return "Attribute [type=" + type + ", value=" + value + "]";
}
@Override
public int compareTo(Attribute that) {
return ComparisonChain.start()
.compare(this.type, that.type)
.compare(this.value, that.value)
.result();
}
}
使用java8:
Comparator.comparing((Person p)->p.firstName)
.thenComparing(p->p.lastName)
.thenComparingInt(p->p.age);
如果你有访问方法:
Comparator.comparing(Person::getFirstName)
.thenComparing(Person::getLastName)
.thenComparingInt(Person::getAge);
如果一个类实现Comparable，那么这个比较器可以用在compareTo方法中:
@Override
public int compareTo(Person o){
return Comparator.comparing(Person::getFirstName)
.thenComparing(Person::getLastName)
.thenComparingInt(Person::getAge)
.compare(this, o);
}
从Steve的回答开始，三元操作符可以使用:
public int compareTo(Person other) {
int f = firstName.compareTo(other.firstName);
int l = lastName.compareTo(other.lastName);
return f != 0 ? f : l != 0 ? l : Integer.compare(age, other.age);
}
