In this article, we will discuss how to sort HashSet in Java 8. Already, in one of the earlier article we discussed about HashSet sorting in ascending & descending order
Key points about HashSet:
- HashSet stores elements in random-order
- Allows only unique element/objects with maximum limit of 1 null
Sorting HashSet in Java 8:
- With simple type like String
- With Object
1. Sorting HashSet with String type
Steps:
- Create new HashSet object
- Add String element/objects to newly created HashSet
- Print original HashSet by iterating using enhanced forEach loop introduced in Java 1.5
- Sort using Java 1.8 stream APIs passing TreeSet as Comparator which does natural ordering of string element/objects, as shown in the below syntax
- Above step returns Collection<String> using Collectors
- Finally iterate through returned Collection<String> using enhanced forEach loop and print to console
Syntax:
Collection<String> collection = hSetCompanies .stream() .collect(Collectors.toCollection(TreeSet::new));
SortingHashSetInJava8.java
package in.bench.resources.collection;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;
public class SortingHashSetInJava8 {
public static void main(String[] args) {
// creating HashSet object of type String
Set<String> hSetCompanies =
new HashSet<String>();
// adding elements to HashSet object
hSetCompanies.add("LinkedIn");
hSetCompanies.add("Amazon");
hSetCompanies.add("Google");
hSetCompanies.add("Apple");
hSetCompanies.add("Facebook");
hSetCompanies.add("Oracle");
hSetCompanies.add("Microsoft");
// Iterating using enhanced for-loop
System.out.println("Random-order: "
+ "Iterating HashSet\n");
for(String company : hSetCompanies) {
System.out.println(company);
}
Collection<String> collection = hSetCompanies
.stream()
.collect(Collectors.toCollection(TreeSet::new));
// Iterating using enhanced for-loop
System.out.println("\n\nAscending Sorting-order: "
+ "Iterating HashSet\n");
for(String company : collection) {
System.out.println(company);
}
}
}
Output:
Random-order: Iterating HashSet LinkedIn Google Apple Microsoft Amazon Oracle Facebook Ascending Sorting-order: Iterating HashSet Amazon Apple Facebook Google LinkedIn Microsoft Oracle
2. Sorting HashSet with Object
Steps:
- First create Employee POJO along with 4-arg parameterized constructor, getter/setter and override toString(); method to print in desired output and compareTo(); method by implementing Comparable interface
- Create new HashSet object and add couple of Employee objects to it
- Print original HashSet by iterating using enhanced forEach loop introduced in Java 1.5 which will invoke toString() method to print in desired format
- Sort using Java 1.8 stream APIs passing class-name as Employee and desired field as getter method of name i.e.; getName() and double-colon (::) separating them, as shown in the below syntax
- Above step returns List<Employee> using Collectors
- Finally iterate through returned List<Employee> using enhanced forEach loop and print to console
Syntax:
// sorting using Java 1.8 stream List<Employee> lstOfEmployee = hSetEmployees.stream() .sorted(Comparator.comparing( Employee::getEmpName)) //comparator .collect(Collectors.toList()); //collector
Employee.java
package in.bench.resources.collection;
public class Employee implements Comparable<Employee> {
// employee members
String empName;
int empId;
int empAge;
String empDesignation;
// 4-arg parameterized constructor
public Employee(String empName, int empId,
int empAge, String empDesignation) {
super();
this.empName = empName;
this.empId = empId;
this.empAge = empAge;
this.empDesignation = empDesignation;
}
// getter & setter
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public int getEmpAge() {
return empAge;
}
public void setEmpAge(int empAge) {
this.empAge = empAge;
}
public String getEmpDesignation() {
return empDesignation;
}
public void setEmpDesignation(String empDesignation) {
this.empDesignation = empDesignation;
}
// override toString() method
@Override
public String toString() {
return "Employee ["
+ "empName=" + empName
+ "\tempId=" + empId
+ "\tempAge=" + empAge
+ "\tempDesignation=" + empDesignation
+ "]";
}
// override compareTo() method
@Override
public int compareTo(Employee emp) {
return this.empName.compareTo(emp.getEmpName());
}
}
SortingHashSetObjectInJava8.java
package in.bench.resources.collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
public class SortingHashSetObjectInJava8 {
public static void main(String[] args) {
// creating HashSet object of type String
Set<Employee> hSetEmployees =
new HashSet<Employee>();
// creating Employee objects
Employee employee2 = new Employee(
"Bill G", 1001, 36, "Consultant");
Employee employee1 = new Employee(
"Mark Z", 1002, 30, "Engineer");
Employee employee4 = new Employee(
"Sundar P", 1003, 32, "Architect");
Employee employee3 = new Employee(
"Larry P", 1004, 25, "Designer");
// adding Employee to HashSet object
hSetEmployees.add(employee1);
hSetEmployees.add(employee2);
hSetEmployees.add(employee3);
hSetEmployees.add(employee4);
// Iterating using enhanced for-loop
System.out.println("Random-order: "
+ "Iterating Employee\n");
hSetEmployees.forEach(
employee -> System.out.println(employee));
// sorting using Java 1.8 stream
List<Employee> lstOfEmployee = hSetEmployees.stream()
.sorted(Comparator.comparing(
Employee::getEmpName)) //comparator
.collect(Collectors.toList()); //collector
// Iterating using enhanced for-loop
System.out.println("\n\nAscending Sorting-order: "
+ "Iterating Employee\n");
lstOfEmployee.forEach(
employee -> System.out.println(employee));
}
}
Output:
Random-order: Iterating Employee Employee [empName=Bill G empId=1001 empAge=36 empDesignation=Consultant] Employee [empName=Sundar P empId=1003 empAge=32 empDesignation=Architect] Employee [empName=Mark Z empId=1002 empAge=30 empDesignation=Engineer] Employee [empName=Larry P empId=1004 empAge=25 empDesignation=Designer] Ascending Sorting-order: Iterating Employee Employee [empName=Bill G empId=1001 empAge=36 empDesignation=Consultant] Employee [empName=Larry P empId=1004 empAge=25 empDesignation=Designer] Employee [empName=Mark Z empId=1002 empAge=30 empDesignation=Engineer] Employee [empName=Sundar P empId=1003 empAge=32 empDesignation=Architect]
Already, we have covered sorting HashSet in different ways prior to Java 1.8 stream APIs, read those article from below links
- Sorting HashSet contents in ascending and descending order
- How to Sort HashSet in Java – 2 ways
- How to sort LinkedHashSet contents in Java ?
Happy Coding !!
Happy Learning !!