Data Structure Transformations

To String

final String employees;

employees = empStream.map(Employee::getName).collect(Collectors.joining(", "));

To Map

final Map<Long, Employee> employees;

employees = empStream.collect(Collectors.toMap(Employee::getId, Function.identity()));

To Map of Lists

final Map<String, List<Employee>> employees;

employees = empStream.collect(Collectors.groupingBy(Employee::getCity));