Following
example shows you how to convert java.util.stream.Stream to a map in Java. By
using toMap method of Collectors class and collect method of Stream class we
can convert java stream to a map.
For example,
1. Get
id, firstName from list employees.
employees.stream().distinct().collect(Collectors.toMap(Employee::getId,Employee::getFirstName));
Above
statement convert list of employees to Map<Integer, String> format.
2. Get id, Employee from all employees.
employees.stream().distinct().collect(Collectors.toMap(Employee::getId,
employee -> employee));
Above
statement convert list of employees to Map<Integer, Employee> format.
Following application illustrate above examples.
Following application illustrate above examples.
import java.util.Objects; public class Employee { private int id; private String firstName; private String lastName; private int age; private String city; private double salary; public Employee(int id, String firstName, String lastName, int age, String city, double salary) { super(); this.id = id; this.firstName = firstName; this.lastName = lastName; this.age = age; this.city = city; this.salary = salary; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getCity() { return city; } public void setCity(String city) { this.city = city; } public double getSalary() { return salary; } public void setSalary(double salary) { this.salary = salary; } @Override public boolean equals(Object employee) { if (Objects.isNull(employee)) return false; if (!(employee instanceof Employee)) return false; Employee emp = (Employee) employee; return id == emp.id; } @Override public int hashCode() { return Objects.hash(id, firstName, lastName, age); } @Override public String toString() { return String.format("%s(%s,%d,%f)", firstName, city, age, salary); } }
import java.util.ArrayList; import java.util.List; import java.util.Map; import java.util.stream.Collectors; public class Test { public static List<Employee> getEmployees() { Employee emp1 = new Employee(1, "Hari Krishna", "Gurram", 26, "Bangalore", 40000); Employee emp2 = new Employee(2, "Joel", "Chelli", 27, "Hyderabad", 50000); Employee emp3 = new Employee(3, "Shanmukh", "Kummary", 28, "Chennai", 35000); Employee emp4 = new Employee(4, "Harika", "Raghuram", 27, "Chennai", 76000); Employee emp5 = new Employee(5, "Sudheer", "Ganji", 27, "Bangalore", 90000); Employee emp6 = new Employee(6, "Rama Krishna", "Gurram", 27, "Bangalore", 56700); Employee emp7 = new Employee(7, "PTR", "PTR", 27, "Hyderabad", 123456); Employee emp8 = new Employee(8, "Siva krishna", "Ponnam", 28, "Hyderabad", 98765); Employee emp9 = new Employee(9, "Raju", "Antony", 40, "Trivendram", 198765); Employee emp10 = new Employee(10, "Brijesh", "Krishnan", 34, "Trivendram", 100000); Employee emp11 = new Employee(9, "Raju", "Antony", 40, "Trivendram", 198765); Employee emp12 = new Employee(10, "Brijesh", "Krishnan", 34, "Trivendram", 100000); List<Employee> employees = new ArrayList<>(); employees.add(emp1); employees.add(emp2); employees.add(emp3); employees.add(emp4); employees.add(emp5); employees.add(emp6); employees.add(emp7); employees.add(emp8); employees.add(emp9); employees.add(emp10); employees.add(emp11); employees.add(emp12); return employees; } public static void main(String args[]) { List<Employee> employees = getEmployees(); /* Get id, Employee from all employees. */ Map<Integer, Employee> map = employees .stream() .distinct() .collect( Collectors.toMap(Employee::getId, employee -> employee)); System.out.println(map + "\n"); /* Get id, firstName from all employees. */ Map<Integer, String> map1 = employees .stream() .distinct() .collect( Collectors.toMap(Employee::getId, Employee::getFirstName)); System.out.println(map1 + "\n"); } }
Output
{1=Hari Krishna(Bangalore,26,40000.000000), 2=Joel(Hyderabad,27,50000.000000), 3=Shanmukh(Chennai,28,35000.000000), 4=Harika(Chennai,27,76000.000000), 5=Sudheer(Bangalore,27,90000.000000), 6=Rama Krishna(Bangalore,27,56700.000000), 7=PTR(Hyderabad,27,123456.000000), 8=Siva krishna(Hyderabad,28,98765.000000), 9=Raju(Trivendram,40,198765.000000), 10=Brijesh(Trivendram,34,100000.000000)} {1=Hari Krishna, 2=Joel, 3=Shanmukh, 4=Harika, 5=Sudheer, 6=Rama Krishna, 7=PTR, 8=Siva krishna, 9=Raju, 10=Brijesh}
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