在Java中使用Comparator时不可编译的源代码
尝试运行此小程序时出现以下错误:
Exception in thread "main" java.lang.ExceptionInInitializerError
at MainClass.main(Person.java:120)
Caused by: java.lang.RuntimeException: Uncompilable source code - FirstNameComparator is not abstract and does not override abstract method compare(java.lang.Object,java.lang.Object) in java.util.Comparator
at FirstNameComparator.<clinit>(Person.java:71)
... 1 more
Java Result: 1
请告诉我我做错了什么,当然这将有助于一个简短的例子,解释如何正确使用Comparator
和Comparable
import java.util.*;
import java.lang.*;
public class Person implements Comparable {
private String firstName;
private String lastName;
private int age;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public void setLastName(String lastName) {
this.lastName= lastName;
}
public String getLastName() {
return lastName;
}
public void setAge(int age) {
this.age=age;
}
public int getAge() {
return age;
}
@Override
public int compareTo(Object anotherPerson) throws ClassCastException {
if(!(anotherPerson instanceof Person)) {
throw new ClassCastException("A person object expected !");
}
int anotherPersonAge = ((Person)anotherPerson).getAge();
return this.age = anotherPersonAge;
}
}
LastNameComparator。爪哇
class LastNameComparator implements Comparator {
public int compareTo(Object person, Object AnotherPerson) {
String lastName1 = ((Person)person).getLastName().toUpperCase();
String firstName1= ((Person)person).getFirstName().toUpperCase();
String lastName2 = ((Person)person).getLastName().toUpperCase();
String firstName2 = ((Person)person).getFirstName().toUpperCase();
if(lastName1.equals(lastName2)) {
return firstName1.compareTo(firstName2);
}else {
return lastName1.compareTo(lastName2);
}
}
}
第一名比较器。爪哇
class FirstNameComparator implements Comparator {
public int compareTo(Object person, Object anotherPerson) {
String lastName1 = ((Person)person).getLastName().toUpperCase();
String firstName1 = ((Person)person).getFirstName().toUpperCase();
String lastName2 = ((Person) person).getLastName().toUpperCase();
String firstName2 = ((Person) person).getFirstName().toUpperCase();
if(firstName1.equals(lastName1)) {
return lastName1.compareTo(lastName2);
}else {
return firstName1.compareTo(firstName2);
}
}
}
主课。爪哇
class MainClass {
public static void main(String[] args) {
Person[] persons = new Person[4];
persons[0] = new Person();
persons[0].setFirstName("Asaftei");
persons[0].setLastName("Ionut");
persons[0].setAge(25);
persons[1] = new Person();
persons[1].setFirstName("Binoclu");
persons[1].setLastName("Telescop");
persons[1].setAge(10);
persons[2] = new Person();
persons[2].setFirstName("Morcov");
persons[2].setLastName("Castravete");
persons[2].setAge(33);
persons[3] = new Person();
persons[3].setFirstName("Rosie");
persons[3].setLastName("Ardei");
persons[3].setAge(55);
System.out.println("Natural Order : ");
for(int counter =0; counter<=3; counter++) {
Person person = persons[counter];
String lastName=person.getLastName();
String firstName=person.getFirstName();
int age = person.getAge();
System.out.println(lastName+ ", " +firstName+ " , "+age);
}
Arrays.sort(persons, new FirstNameComparator());
System.out.println();
System.out.println("Sorted by First Name: ");
for(int counter=0; counter<=3; counter++) {
Person person = persons[counter];
String lastName = person.getLastName();
String firstName = person.getFirstName();
int age = person.getAge();
System.out.println(lastName+ ", " +firstName+ ", " +age );
}
Arrays.sort(persons, new LastNameComparator());
System.out.println();
System.out.println("Sorted by Last Name"); for(int counter=0; counter<=3; counter++) {
Person person = persons[counter];
String lastName = person.getLastName().toUpperCase();
String firstName = person.getFirstName().toUpperCase();
int age = person.getAge();
System.out.println(lastName +", "+firstName+", "+age);
}
}
}
# 1 楼答案
^{} 需要实现^{} 方法,而不是
compareTo
方法因此,例如,您的
FirstNameComparator
应该如下所示:请注意,由于此
Comparator
用于比较Person
实例,因此最好使用泛型语法并将其定义为:# 2 楼答案
别忘了^{} 接受generic type arguments。
因此,请使用
implements Comparable<Person>
。这意味着你可以比较两个人此外,不允许重写方法向该方法添加其他抛出。见this question
新的定义应该是这样的: