I have a List<User> userList need to convert to UserData[]
for(int i = 0; i < userList.size(); i++){
userData[i] = userList.get(i);
}
It always returns null though the list size is 1. can anyone help on this.
3 Answers
Collections can be converted to arrays:
UserData[] userArray = userList.toArray(new UserData[userList.size()])
5 Comments
dumbPotato21
won't work.
toArray returns Object[]
Ted Cassirer
Correct, sorry about that
dumbPotato21
Would work, but
new UserData[0] is faster. Apart from that, it's userList.size()
Rathishkumar
@ChandlerBing i tried with your solution i get ArrayIndexOutof BoundException error
Rathishkumar
this solved the issue i directly added to the setters so i accept this answer
just another option, this time using the power of java8 streams:
List<Foo> myList = Arrays.asList(new Foo(), new Foo(), new Foo(), new Foo());
Foo[] stringArray = myList.stream().toArray(Foo[]::new);
Edit:
Stream is actually not necessary so you can still do:
Foo[] fooArray = myList.toArray(new Foo[0])
answered Jun 1, 2017 at 13:52
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1 Comment
LazerBanana
not really necessary to use a stream here. Foo[] fooArray = myList.toArray(new Foo[0]);
Here is the code try this
import java.util.ArrayList;
public class ArrayListTest {
static UserData[] userdata = new UserData[3];
public static void main(String[] args) {
ArrayListTest alt = new ArrayListTest();
ArrayList<UserData> users = alt.arrayTest();
for (int i = 0; i < users.size(); i++) {
userdata[i] = users.get(i);
}
for (UserData ud : userdata) {
System.out.println("User Name " + ud.getName());
}
}
private ArrayList<UserData> arrayTest() {
ArrayList<UserData> userList = new ArrayList<>();
userList.add(new UserData("user 1"));
userList.add(new UserData("user 2"));
userList.add(new UserData("user 3"));
return userList;
}
private class UserData {
private final String name;
public UserData(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
}
null? Also, show us the declarations and initializations ofuserData[]anduserList, please.returnstatementnull” What, exactly, returns null? Nothing in the code you’ve shown can “return” anything.