Basic example using SparseArray

class Person {
    String name;

    public Person(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Person person = (Person) o;

        return name != null ? name.equals(person.name) : person.name == null;
    }

    @Override
    public int hashCode() {
        return name != null ? name.hashCode() : 0;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

final Person steve = new Person("Steve");
Person[] persons = new Person[] { new Person("John"), new Person("Gwen"), steve, new Person("Rob") };
int[] identifiers = new int[] {1234, 2345, 3456, 4567};

final SparseArray<Person> demo = new SparseArray<>();

// Mapping persons to identifiers.
for (int i = 0; i < persons.length; i++) {
    demo.put(identifiers[i], persons[i]);
}

// Find the person with identifier 1234.
Person id1234 = demo.get(1234); // Returns John.

// Find the person with identifier 6410.
Person id6410 = demo.get(6410); // Returns null.

// Find the 3rd person.
Person third = demo.valueAt(3); // Returns Rob.

// Find the 42th person.
//Person fortysecond = demo.valueAt(42); // Throws ArrayIndexOutOfBoundsException.

// Remove the last person.
demo.removeAt(demo.size() - 1); // Rob removed.

// Remove the person with identifier 1234.
demo.delete(1234); // John removed.

// Find the index of Steve.
int indexOfSteve = demo.indexOfValue(steve);

// Find the identifier of Steve.
int identifierOfSteve = demo.keyAt(indexOfSteve);