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| 9. 1. 6. 利用比较和比较 |
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- Implementing java.lang.Comparable enables you to define one way to compare instances of your class.
- Objects sometimes might be comparable in more ways.
- Comparator defines how two objects should be compared.
- To make objects comparable in two ways, you need two comparators.
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import java.util.Arrays;
import java.util.Comparator;
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 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 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;
}
}
class LastNameComparator implements Comparator {
public int compare(Object person, Object anotherPerson) {
String lastName1 = ((Person) person).getLastName().toUpperCase();
String firstName1 = ((Person) person).getFirstName().toUpperCase();
String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
String firstName2 = ((Person) anotherPerson).getFirstName().toUpperCase();
if (lastName1.equals(lastName2)) {
return firstName1.compareTo(firstName2);
} else {
return lastName1.compareTo(lastName2);
}
}
}
class FirstNameComparator implements Comparator {
public int compare(Object person, Object anotherPerson) {
String lastName1 = ((Person) person).getLastName().toUpperCase();
String firstName1 = ((Person) person).getFirstName().toUpperCase();
String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
String firstName2 = ((Person) anotherPerson).getFirstName().toUpperCase();
if (firstName1.equals(firstName2)) {
return lastName1.compareTo(lastName2);
} else {
return firstName1.compareTo(firstName2);
}
}
}
public class MainClass {
public static void main(String[] args) {
Person[] persons = new Person[4];
persons[0] = new Person();
persons[0].setFirstName("A");
persons[0].setLastName("X");
persons[0].setAge(56);
persons[1] = new Person();
persons[1].setFirstName("S");
persons[1].setLastName("C");
persons[1].setAge(8);
persons[2] = new Person();
persons[2].setFirstName("E");
persons[2].setLastName("H");
persons[2].setAge(16);
persons[3] = new Person();
persons[3].setFirstName("B");
persons[3].setLastName("Q");
persons[3].setAge(69);
System.out.println("Natural Order");
for (int i = 0; i < 4; i++) {
Person person = persons[i];
String lastName = person.getLastName();
String firstName = person.getFirstName();
int age = person.getAge();
System.out.println(lastName + ", " + firstName + ". Age:" + age);
}
Arrays.sort(persons, new LastNameComparator());
System.out.println();
System.out.println("Sorted by last name");
for (int i = 0; i < 4; i++) {
Person person = persons[i];
String lastName = person.getLastName();
String firstName = person.getFirstName();
int age = person.getAge();
System.out.println(lastName + ", " + firstName + ". Age:" + age);
}
Arrays.sort(persons, new FirstNameComparator());
System.out.println();
System.out.println("Sorted by first name");
for (int i = 0; i < 4; i++) {
Person person = persons[i];
String lastName = person.getLastName();
String firstName = person.getFirstName();
int age = person.getAge();
System.out.println(lastName + ", " + firstName + ". Age:" + age);
}
Arrays.sort(persons);
System.out.println();
System.out.println("Sorted by age");
for (int i = 0; i < 4; i++) {
Person person = persons[i];
String lastName = person.getLastName();
String firstName = person.getFirstName();
int age = person.getAge();
System.out.println(lastName + ", " + firstName + ". Age:" + age);
}
}
}
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Natural Order
X, A. Age:56
C, S. Age:8
H, E. Age:16
Q, B. Age:69
Sorted by last name
C, S. Age:8
H, E. Age:16
Q, B. Age:69
X, A. Age:56
Sorted by first name
X, A. Age:56
Q, B. Age:69
H, E. Age:16
C, S. Age:8
Sorted by age
C, S. Age:8
H, E. Age:16
X, A. Age:56
Q, B. Age:69 |
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