In this Collection framework tutorial we will learn how to sort arrays(by implementing Comparator and Comparator) with lots of examples and programs in java.
Contents of page :
- Example/Program 1 to sort Integer array using Arrays.sort (by default Arrays.sort will sort array in ascending order) in java
- Example/Program 2 to sort Integer array by using Arrays.sort (we will define Comparator to sort elements in descending order) in java
- Example/Program 3 to sort Employee array using Arrays.sort in ascending order on basis of name and id by implementing Comparator interface in java
- Example/Program 4 to understand Comparator of superclass can be used by subclasses in java.
Merge sort calls overridden compare method of Comparator interface for comparison of values (if any).
Must know fact :
If number of elements is less than 7 then Insertion Sort is used rather than Merge Sort (because in case elements are less than 7 it offers better time complexity) in java.
Example/Program 1 to sort Integer array using Arrays.sort (by default Arrays.sort will sort array in ascending order) in java
import java.util.Arrays;
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal JavaMadeSoEasy.com
* Main class
*/
public class ArraysSortExample {
public static void main(String...a){
Integer intArray[]={2,3,1};
System.out.print("Array before sorting : ");
for(int i: intArray){
System.out.print(i+" ");
}
Arrays.sort(intArray);
System.out.print("\nArray after sorting : ");
for(int i: intArray){
System.out.print(i+" ");
}
}
}
/*OUTPUT
Array before sorting : 2 3 1
Array after sorting : 1 2 3
*/
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Example/Program 2 to sort Integer array by using Arrays.sort (we will define Comparator to sort elements in descending order) in java
import java.util.Arrays;
import java.util.Comparator;
class SortDescending implements Comparator<Integer> {
@Override
public int compare(Integer o1, Integer o2) {
//using Comparator to sort array in descending order.
return o2.compareTo(o1);
}
}
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal JavaMadeSoEasy.com
* Main class
*/
public class ArraysSortExample {
public static void main(String...a){
Integer intArray[]={2,3,1};
System.out.print("Array before sorting : ");
for(int i: intArray){
System.out.print(i+" ");
}
Arrays.sort(intArray, new SortDescending());
System.out.print("\nArray after sorting in descending order : ");
for(int i: intArray){
System.out.print(i+" ");
}
}
}
/*OUTPUT
Array before sorting : 2 3 1
Array after sorting in descending order : 3 2 1
*/
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Example/Program 3 to sort Employee array using Arrays.sort in ascending order on basis of name and id by implementing Comparator interface in java
import java.util.Arrays;
import java.util.Comparator;
class Employee{
String name;
String id;
public Employee() {}
public Employee(String name, String id) {
this.name = name;
this.id = id;
}
@Override
public String toString() {
return "Employee{" + "name=" + name + ", id=" + id + '}';
}
}
class ComparatorName implements Comparator<Employee>{
@Override
public int compare(Employee obj1, Employee obj2) {
//sort Employee on basis of name(ascending order)
return obj1.name.compareTo(obj2.name);
}
}
class ComparatorId implements Comparator<Employee>{
@Override
public int compare(Employee obj1, Employee obj2) {
//sort Employee on basis of id(ascending order)
return obj1.id.compareTo(obj2.id);
}
}
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal JavaMadeSoEasy.com
* Main class
*/
public class ArraysSortExample {
public static void main(String[] args) {
Employee emp1 = new Employee("sam", "4");
Employee emp2 = new Employee("amy", "2");
Employee emp3 = new Employee("brad", "1");
Employee employeeArray[] = { emp1, emp2, emp3 };
System.out.print(" employeeArray Before sorting : \n");
for (Employee emp : employeeArray) {
System.out.print(emp + " ");
}
Arrays.sort(employeeArray, new ComparatorName());
System.out.println("\n\n employeeArray after sorting on basis of "
+ "name(ascending order) : ");
for (Employee emp : employeeArray) {
System.out.print(emp + " ");
}
Arrays.sort(employeeArray, new ComparatorId());
System.out.println("\n\n employeeArray after sorting on basis of "
+ "id(ascending order) : ");
for (Employee emp : employeeArray) {
System.out.print(emp + " ");
}
}
}
/*OUTPUT
employeeArray Before sorting :
[Employee{name=sam, id=4}, Employee{name=amy, id=2}, Employee{name=brad, id=1}]
employeeArray after sorting on basis of name(ascending order) :
[Employee{name=amy, id=2}, Employee{name=brad, id=1}, Employee{name=sam, id=4}]
employeeArray after sorting on basis of id(ascending order) :
[Employee{name=brad, id=1}, Employee{name=amy, id=2}, Employee{name=sam, id=4}]
*/
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Example/Program 4 to understand Comparator of superclass can be used by subclasses in java
Animal is superclass of Dog and Lion.
dogArray is array of dogs.
AnimalComparator is a Comparator of Animal class [ class AnimalComparator implements Comparator<Animal> ]
We will be using Arrays.sort(dogArray, new AnimalComparator()); in program.
Method definition of sort method in java.util.Arrays is -
public static <T> void sort(T[] a, Comparator<? super T> c)
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So, what do you mean by second parameter Comparator<? super T> c
Let’s understand first parameter -
T[] a
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dogArray has been passed as parameter which is array of Dog, and Dog extends Animal. So,
T is Dog, and
T[] is dogArray.
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Now, let’s understand second parameter -
Comparator<? super T> c
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In the program, following 2 lines have been used >
class Dog extends Animal (Animal is superclass of Dog),
class AnimalComparator implements Comparator<Animal>
(AnimalComparator is a Comparator of Animal class but it can be used by subclasses (i.e. Dog and Lion) as well.)
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Full program -
import java.util.Arrays;
import java.util.Comparator;
/**
* Animal class
*/
class Animal{
Integer height;
}
/**
* Lion class
*/
class Lion extends Animal{
Lion(Integer height){
this.height=height;
}
@Override
public String toString() {
return "Lion [height=" + height + "]";
}
}
/**
* Dog class
*/
class Dog extends Animal{
Dog(Integer height){
this.height=height;
}
@Override
public String toString() {
return "Dog [height=" + height + "]";
}
}
/**
* Comparator to sort animal's height in ascending order.
*/
class AnimalComparator implements Comparator<Animal> {
@Override
public int compare(Animal o1, Animal o2) {
//using Comparator to sort animal's height in ascending order.
return o1.height.compareTo(o2.height);
}
}
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal JavaMadeSoEasy.com
* Main class
*/
public class ArraysSortExample {
public static void main(String...a){
System.out.println("-----Sorting Lion's height -- using AnimalComparator-----");
Lion lion1=new Lion(3);
Lion lion2=new Lion(1);
Lion lion3=new Lion(2);
Lion lionArray[]={lion1, lion2, lion3};
System.out.print(" lionArray before sorting : \n");
for (Animal animal : lionArray) {
System.out.print(animal + " ");
}
Arrays.sort(lionArray, new AnimalComparator());
System.out.println("\n\n lionArray after sorting on basis of "
+ "height(ascending order) : ");
for (Animal animal : lionArray) {
System.out.print(animal + " ");
}
System.out.println("\n\n\n------Sorting Dog's height -- using AnimalComparator----");
Dog dog1=new Dog(2);
Dog dog2=new Dog(1);
Dog dog3=new Dog(3);
Dog dogArray[]={dog1, dog2, dog3};
System.out.print(" dogArray before sorting : \n");
for (Animal animal : dogArray) {
System.out.print(animal + " ");
}
Arrays.sort(dogArray, new AnimalComparator());
System.out.println("\n\n dogArray after sorting on basis of "
+ "height(ascending order) : ");
for (Animal animal : dogArray) {
System.out.print(animal + " ");
}
}
}
/*OUTPUT
----------Sorting Lion's height -- using AnimalComparator----------
lionArray before sorting :
Lion [height=3] Lion [height=1] Lion [height=2]
lionArray after sorting on basis of height(ascending order) :
Lion [height=1] Lion [height=2] Lion [height=3]
--------Sorting Dog's height -- using AnimalComparator---------
dogArray before sorting :
Dog [height=2] Dog [height=1] Dog [height=3]
dogArray after sorting on basis of height(ascending order) :
Dog [height=1] Dog [height=2] Dog [height=3]
*/
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So in this Collection framework tutorial we learned how to sort arrays(by implementing Comparator and Comparator) with lots of examples and programs in java.
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