Detailed explanation of JAVA using Comparator interface to realize custom sorting
- 2021-07-09 08:17:04
- OfStack
1. Principles
The Comparator interface enables custom sorting, and when implementing the Comparator interface, override the compare method:
int compare (Object o1, Object o2) Returns an integer of 1 basic type
If you want to sort in ascending order, o1 is less than o2 and returns-1 (negative number), equal returns 0, and 01 is greater than 02 and returns 1 (positive number)
If you want to sort in descending order, o1 is less than o2 and returns 1 (positive number), equal returns 0, and 01 is greater than 02 and returns-1 (negative number)
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class UserComparator implements Comparator < User > {
public static void main( String[] args ) {
List < User > users = new ArrayList < User >();
users.add( new User( 10, "a" ) );
users.add( new User( 11, "d" ) );
users.add( new User( 15, "s" ) );
users.add( new User( 6, "x" ) );
users.add( new User( 17, "a" ) );
users.add( new User( 17, "b" ) );
users.add( new User( 17, "c" ) );
users.add( new User( 17, "d" ) );
UserComparator comparator = new UserComparator();
users.sort( comparator );
// You can also use: Collections.sort( users, comparator );
for ( User u : users ) {
System.out.println( u );
}
}
@Override
public int compare( User u1, User u2 ) {
if ( u1.equals( u2 ) ) {
return 0;
}
else if ( u1.getAge() < u2.getAge() ) {
return 1;
}
else if ( u1.getAge() == u2.getAge() ) {
int f = u1.getName().compareTo( u2.getName() );
if ( f < 0 ) {
return -1;
}
return 0;
}
else {
return -1;
}
}
}
class User {
private int age;
private String name;
public User() {
}
public User( int age, String name ) {
this.age = age;
this.name = name;
}
public int getAge() {
return age;
}
public void setAge( int age ) {
this.age = age;
}
public String getName() {
return name;
}
public void setName( String name ) {
this.name = name;
}
@Override
public String toString() {
return "User [age=" + age + ", name=" + name + "]";
}
}
User [age=17, name=a]
User [age=17, name=b]
User [age=17, name=c]
User [age=17, name=d]
User [age=15, name=s]
User [age=11, name=d]
User [age=10, name=a]
User [age=6, name=x]