How to Sort a Collection in Java




Consider a list of Person object. There are two ways to sort the list . Using Comparator or Comparable. 




class Person implements Comparable{

  public String name;

  public String lastName;

 

  public Person(String name, String lastName){

     this.name=name;

     this.lastName=lastName;

  }

  public String getName(){

    return name;

  }

  public String getLastName(){

    return lastName;

  }

 

  public int compareTo(Object obj){

    Person p = (Person)obj;

    return this.name.compareTo(p.getName);

  }

  public static void main(String arg[]){

        List myList = new ArrayList();

 

    myList.add(new Person("Robert","USA"));

    myList.add(new Person("Andy","UK"));

    myList.add(new Person("Harish","India"));

    Collections.sort(myList);

    for(Person person : myList){

     System.out.println("My name is "+person.getName());

    }

  }

 }

  Output is :

  My name is Andy

  My name is Harish

  My name is Robert







public sortList()  {

 

     List personList = getListofPerson(); // some method to get the list.

     //sort by name;

   Collections.sort(personList, new Comparator() {

           public int compare(Person e1, Person e2) {

               return e2.name.compareTo(e1.name);

         }});

   // sort by age

     

     Collections.sort(personList, new Comparator() {

           public int compare(Person e1, Person e2) {

                if (e1.age > e2.age )

                return 1;

                if (e1.age < e2.age)

                 return -1;

                else

                    return 0;

         }});

 }