Get an element from arrayList inside another class

Question

I have a Staff class which contains a list of roles for that particular staff member. I also have staffList which holds the staff objects.

How do I get an element from the rolesList for that specific instance of the class?

I have tried:

staffList.get(0).getRolesList().get(0)

Which should be the first element of the rolesList from the first element of the staffList, but it just ruturns null.

I also tried:

rolesList.get(staffList.get(0))
rolesList.getIndexOf(staffList.get(0).getRolesList.get(0)

All return null

If I just get the value direct from the rolesList using get index it will display no problem.

I think it is getting a version of the rolesList but not the one that is in that particular Staff object

I have created a new Staff Member and a role in the roleList then used the list when I construct the staff object, so using the getRolesList method of that object and then get the index it should return the value from within the roleList but it isn't:

private List<Staff> staffList = new ArrayList();
ArrayList<Role> roleList = new ArrayList();
roleList.add(Role.DRIVER);
testDriver = new Staff("Mike", "Joy", roleList);
testStaffList.add(testDriver);

GetRolesList() Code

public List<Role> getRoleList() {
        return roleList;
    }

I basically want to get the stored Role from the objects rolelist within the testdriver object.

testDriver --> roleList --> Role.DRIVER (or whatever the Role happens to be)

As i can see on the last pieces of code, `staffList` is not related with the other objects at any point. Are you missing to paste something else? — Lucio, Aug 14 '16 at 01:38
Could you paste code from the `getRolesList()` function? It is unclear what the problem is without further examples of the code you have used — dunck, Aug 14 '16 at 01:39

score 0 · Accepted Answer · edited May 23 '17 at 11:51

(a) We do not see the line of code adding testDriver to the staffList.

staffList.add( testDriver );

(b) You are missing parens on your call to getRolesList.

(c) You need to do some basic debugging. In the debugger or in extra code, look at:

size of staffList
Staff s = staffList.get(0)
List roles = s.getRolesList()
size of roles

Bonus tip… Apparently you are using an enum for Role. If so, you should consider using an EnumSet rather than a List for less memory usage and faster execution. EnumSet is a specialized implementation of Set. More discussion on another Question. Not part of your problem, just a tip.

Set<Role> roles = EnumSet.of( Role.DRIVER , Role.MECHANIC );
Staff testDriver = new Staff( "Mike" , "Joy" , roles );

score 0 · Answer 2 · answered Aug 14 '16 at 02:53

0

Could you give your full source.. That's not clear. I think u wanna add your staff object into staff list.. If it is

Stafflist.add(new Staff("a","b",role list));

Add all you want Then try to get ..

answered Aug 14 '16 at 02:53

George Princelin J

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Get an element from arrayList inside another class

2 Answers2