Ignore duplicates while producing map from a stream

Using merge function, we can specify how to resolve collisions associated with same key.

Example

Map<String, String> map = emps.stream()

.collect(Collectors.toMap(Employee::getFirstName, Employee::getLastName, (value1, value2) -> {

         return value1;

}));

Above snippet specifies in case of collisions take first value.

Employee.java

package com.sample.app.model;

public class Employee {
 private String firstName;
 private String lastName;

 public Employee(String firstName, String lastName) {
  super();
  this.firstName = firstName;
  this.lastName = lastName;
 }

 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;
 }

 @Override
 public int hashCode() {
  final int prime = 31;
  int result = 1;
  result = prime * result + ((firstName == null) ? 0 : firstName.hashCode());
  result = prime * result + ((lastName == null) ? 0 : lastName.hashCode());
  return result;
 }

 @Override
 public boolean equals(Object obj) {
  if (this == obj)
   return true;
  if (obj == null)
   return false;
  if (getClass() != obj.getClass())
   return false;
  Employee other = (Employee) obj;
  if (firstName == null) {
   if (other.firstName != null)
    return false;
  } else if (!firstName.equals(other.firstName))
   return false;
  if (lastName == null) {
   if (other.lastName != null)
    return false;
  } else if (!lastName.equals(other.lastName))
   return false;
  return true;
 }

}

App.java

package com.sample.app;

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import com.sample.app.model.Employee;

public class App {

 public static void main(String args[]) throws InterruptedException {
  Employee emp1 = new Employee("Ram", "Gurram");
  Employee emp2 = new Employee("Siva", "Ponnam");
  Employee emp3 = new Employee("Sailaja", "Navakotla");
  Employee emp4 = new Employee("Ram", "Battu");

  List<Employee> emps = Arrays.asList(emp1, emp2, emp3, emp4);

  Map<String, String> map = emps.stream()
    .collect(Collectors.toMap(Employee::getFirstName, Employee::getLastName, (value1, value2) -> {
     return value1;
    }));

  for (String firstName : map.keySet()) {
   System.out.println(firstName + " , " + map.get(firstName));
  }
 }

}

Output

Sailaja , Navakotla

Siva , Ponnam

Ram , Gurram

You may like

Miscellaneous

Interview Questions

Programming Questions

Create file parent directories if they are not exist

Convert iterator to list

How to check BigDecimal is greater than 0?

How to compare two BigDecimals?

Convert list to map using streams