I’m going to
explain these concepts using Student example.I have added
extra variable “place” where you can see the data sorted way.
import java.util.Comparator;
public class Student implements Comparable<Student>{
private int id;
private String name;
private int age;
private int place;//to identify the place change against the sort
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(int id, String name, int age, int place) {
super();
this.id = id;
this.name = name;
this.age = age;
this.place = place;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getPlace() {
return place;
}
public void setPlace(int place) {
this.place = place;
}
//implementation of compareTo method in Comparable interface
public int compareTo(Student s) {
return this.id-s.id;
}
//implementation of Comparator interface according to sort by age
public static Comparator<Student> ageComparator = new Comparator<Student>(){
public int compare(Student s0, Student s1) {
return s0.getAge()-s1.getAge();
}
};
//implementation of Comparator interface according to sort by name
public static Comparator<Student> nameComparator = new Comparator<Student>(){
public int compare(Student s0, Student s1) {
return s0.getName().compareTo(s1.getName());
}
};
//implementation of Comparator interface according to sort by id then name
public static Comparator<Student> idNameComparator = new Comparator<Student>(){
public int compare(Student s0,Student s1){
int flag = s0.id-s1.id;
if(flag == 0)
flag = s0.getName().compareTo(s1.getName());
return flag;
}
};
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", age=" + age + ",place = "+place+"]";
}
}
public class App
{
public static void main( String[] args )
{
testCompare();
}
public static void testCompare(){
Student s2 = new Student(2,"disa",24,1);
Student s5 = new Student(5,"ciri",20,2);
Student s3 = new Student(3,"amal",30,3);
Student s1 = new Student(1,"biri",10,4);
List<Student> al = new ArrayList<Student>();
al.add(s2);
al.add(s5);
al.add(s3);
al.add(s1);
System.out.println("Unsorted ArrayList");
for (Student s : al) {
System.out.println(s.toString());
}
System.out.println("");
System.out.println("Sorted using Comparable interface accroding to compareTo() method");
Collections.sort(al);
for (Student s : al) {
System.out.println(s.toString());
}
System.out.println("");
System.out.println("Sorted using Comparator interface accroding to ageComparator's compare() method");
Collections.sort(al,Student.ageComparator);
for (Student s : al) {
System.out.println(s.toString());
}
System.out.println("");
System.out.println("Sorted using Comparator interface accroding to nameComparator's compare() method");
Collections.sort(al,Student.nameComparator);
for (Student s : al) {
System.out.println(s.toString());
}
System.out.println("");
System.out.println("Sorted using Comparator interface accroding to idNameComparator's compare() method");
Collections.sort(al,Student.idNameComparator);
for (Student s : al) {
System.out.println(s.toString());
}
}
}
Output
Unsorted ArrayList
Student [id=2, name=disa, age=24,place = 1]
Student [id=5, name=ciri, age=20,place = 2]
Student [id=3, name=amal, age=30,place = 3]
Student [id=1, name=biri, age=10,place = 4]
Sorted using Comparable interface accroding to compareTo() method
Student [id=1, name=biri, age=10,place = 4]
Student [id=2, name=disa, age=24,place = 1]
Student [id=3, name=amal, age=30,place = 3]
Student [id=5, name=ciri, age=20,place = 2]
Sorted using Comparator interface accroding to ageComparator's compare() method
Student [id=1, name=biri, age=10,place = 4]
Student [id=5, name=ciri, age=20,place = 2]
Student [id=2, name=disa, age=24,place = 1]
Student [id=3, name=amal, age=30,place = 3]
Sorted using Comparator interface accroding to nameComparator's compare() method
Student [id=3, name=amal, age=30,place = 3]
Student [id=1, name=biri, age=10,place = 4]
Student [id=5, name=ciri, age=20,place = 2]
Student [id=2, name=disa, age=24,place = 1]
Sorted using Comparator interface accroding to idNameComparator's compare() method
Student [id=1, name=biri, age=10,place = 4]
Student [id=2, name=disa, age=24,place = 1]
Student [id=3, name=amal, age=30,place = 3]
Student [id=5, name=ciri, age=20,place = 2]
