How to find by data variable from list of object in java

Question

Recently I had a technical discussion in one interview process. He asked me below scenario,

Class Employee
{
   int empId;
   String empName;
   String salary;
}

Now I'm storing 1000 (This could go high) employee object in an Arraylist. What is the best way in terms of time complexity, wherein I could search by empName from this list.

Can anyone please suggest the best possible way for this...?

amit · Accepted Answer · 2020-07-16 14:15:18Z

1

You could store the elements in a HashMap<String, Employee>, which is indexed by the employee name, and the value contains the Employee object.

This gives you O(1) (average case) lookup for ID lookup.

Another option, if you wish to keep using your ArrayList to store the objects, is to have it sorted (using a custom Comparator) by the empName, and then find the relevant item in O(logn) using Collections.binarySearch()

answered Jul 16, 2020 at 14:15

amit

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2 Comments

Rakesh Prajapati Over a year ago

I suggested this answer, but then he changed the question by saying now I want to search by empId, would you create new map implementation for it..? And after that I suggested if that is the case we'll sort it out and then we'll loop it in and search to avoid any further records to traverse... But then he said okay leave it lets move ahead...

amit Over a year ago

If you want to start looking for all, or many, of the fields in your object, you are looking for some kind of SQL like DS, Read more about Relational databases

tn-nguyen · Accepted Answer · 2020-07-16 14:20:45Z

1

employees.stream().filter(e -> "name".equals(e.getEmpName())).collect(Collectors.toList());

using stream api and filter java 8

answered Jul 16, 2020 at 14:20

tn-nguyen

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