Krieger Krieger - 19 days ago 8
Java Question

How to get duplicate elements in array list using guava predicates

I have a array with set of elements. I need to find the duplicate elements in that array by comparing particular field using guava predicated in java.

For example:

I have an arraylist with set of employees details. I need to find details of employees with same name.

Answer

You can use Guava Multimaps.index method:

ImmutableListMultimap<String, Employee> byName = 
  Multimaps.index(employees, new Function<Employee, String>(){
      @Override
      public String apply(Employee e) {
          return e.getName();
      } 
  });

In Java 8:

Map<Department, List<Employee>> byName = 
    employees.stream()
             .collect(Collectors.groupingBy(Employee::getName))

Regarding your comment, it seems that you want to filter the list to keep only employees with a specific name.

So using Guava:

List<Employee> employees = // ...
Collection<Employee> filtered = 
    Collections2.filter(employees, new Predicate<Employee>() {
        @Override
        public boolean apply(Employee e) {
            return e.getName().equals("John Doe");
        }
    });
// if you want a List:
List<Employee> filteredList = new ArrayList<>(filtered);

Using Java 8:

List<Employee> filteredList = employees.stream()
                                       .filter(e -> e.getName().equals("John Doe"))
                                       .collect(Collectors.toList());
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