List<Customer> customers = findAllCustomer();
public class Customer implements Serializable {
private State state;
//getter and setter
I have below approached using jdk 7
List<State> states = new ArrayList<>();
for (Customer customer : customers) {
states.add(customer.getState());
}
How can I achieve the same thing using jdk 8?
Stream the contents, map to get the state and collect it as a List.
customers.stream()
.map(Customer::getState)
.collect(Collectors.toList());
If you need an ArrayList as the resultant list
customers.stream()
.map(Customer::getState)
.collect(Collectors.toCollection(ArrayList::new));
List<State> states = new ArrayList<>();
customers
.stream()
.map(Customer::getState)
.forEach(states::add);
Using Lambda and forEach
customers.forEach(p -> {
states.add(p.getState())
}
);
List<State> states = customers.stream()
.map(Customer::getState)
.collect(Collectors.toList());
Additionally you can wrap this issue to the static method:
public static List<State> getCustomerStates(List<Customer> customers) {
return customers.stream()
.map(Customer::getState)
.collect(Collectors.toList());
}
...or to the function:
private static final Function<List<Customer>, List<State>> getCustomerStates =
customers -> customers.stream()
.map(Customer::getState)
.collect(Collectors.toList());
getCustomerStates with assignment operator.Worth to mentions that if the state is actually a List<state> (states)
public class Customer implements Serializable {
private List<State> states;//Important note: I changed State to a List<State> here
//getter and setter
It will be a little bit tricky to get a List of states here
List<State> states = customers.stream()
.map(Customer::getStates)
.filter(Objects::nonNull)//null check
.flatMap(Collection::stream)
.collect(Collectors.toList());
states.add wouldn't have worked. The OP should have used addAll
add and addAll?state cannot be a List. So, this doesn't answer the current questionWorth to mentions that if... and I actually did define a List<State> states in the first code part? Is it not enough?