Approach 1: By traversing each element of the list.
Map<Integer, Employee> map1 = new HashMap<>();
for (Employee emp : emps) {
map1.put(emp.getId(), emp);
}
Approach 2: Using stream() method
Map<Integer, Employee> map2 = emps.stream()
.collect(Collectors.toMap(Employee::getId, emp -> emp, (empObj1, empObj2) -> {
return empObj1;
}));
Approach 3: Using parallelStream() method
Map<Integer, Employee> map3 = emps.parallelStream()
.collect(Collectors.toMap(Employee::getId, item -> item, (empObj1, empObj2) -> {
return empObj1;
}));
Find the below working application.
App.java
package com.sample.app;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
import com.sample.app.model.Employee;
public class App {
private static void printMap(Map<Integer, Employee> map) {
Set<Integer> set = map.keySet();
for (int key : set) {
System.out.println(map.get(key));
}
System.out.println("-----------------------------");
}
public static void main(String args[]) {
Employee emp1 = new Employee(1, "Krishna", "Gurram");
Employee emp2 = new Employee(2, "Narasimha", "Rao");
Employee emp3 = new Employee(3, "Ram", "Pothineni");
Employee emp4 = new Employee(4, "Jaidepp", "Geera");
Employee emp5 = new Employee(5, "Joel", "Chelli");
List<Employee> emps = Arrays.asList(emp1, emp2, emp3, emp4, emp5);
Map<Integer, Employee> map1 = new HashMap<>();
for (Employee emp : emps) {
map1.put(emp.getId(), emp);
}
Map<Integer, Employee> map2 = emps.stream()
.collect(Collectors.toMap(Employee::getId, emp -> emp, (empObj1, empObj2) -> {
return empObj1;
}));
Map<Integer, Employee> map3 = emps.parallelStream()
.collect(Collectors.toMap(Employee::getId, item -> item, (empObj1, empObj2) -> {
return empObj1;
}));
printMap(map1);
printMap(map2);
printMap(map3);
}
}
Output
Employee [id=1, firstName=Krishna, lastName=Gurram]
Employee [id=2, firstName=Narasimha, lastName=Rao]
Employee [id=3, firstName=Ram, lastName=Pothineni]
Employee [id=4, firstName=Jaidepp, lastName=Geera]
Employee [id=5, firstName=Joel, lastName=Chelli]
-----------------------------
Employee [id=1, firstName=Krishna, lastName=Gurram]
Employee [id=2, firstName=Narasimha, lastName=Rao]
Employee [id=3, firstName=Ram, lastName=Pothineni]
Employee [id=4, firstName=Jaidepp, lastName=Geera]
Employee [id=5, firstName=Joel, lastName=Chelli]
-----------------------------
Employee [id=1, firstName=Krishna, lastName=Gurram]
Employee [id=2, firstName=Narasimha, lastName=Rao]
Employee [id=3, firstName=Ram, lastName=Pothineni]
Employee [id=4, firstName=Jaidepp, lastName=Geera]
Employee [id=5, firstName=Joel, lastName=Chelli]
-----------------------------
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