如何从contactList更快地搜索给定的字符串

Question

I have ContactList which contains contacts with firstName and lastName. I want to perform search by FirstName or lastName.

I have already written code which works fine but I want to improve search in terms of speed and memory.

public class Contact implements Comparable<Contact> {

    private String firstName;
    private String lastName;
    private String name;

    public Contact(String name) {

        this.name = name;
        if (name.contains(" ")) {
            this.firstName = name.split("\\s+")[0];
            this.lastName = name.split("\\s+")[1];
        } else {
            this.firstName = name;
            this.lastName = "";
        }
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Contact{" + name + '}';
    }

    @Override
    public int compareTo(Contact contact) {
        System.out.println("in compareto");
        return this.name.compareToIgnoreCase(contact.getName());
    }
@Override
public int hashCode() {
    return (firstName.hashCode() * (lastName != null ? lastName.hashCode() : 0));
}

@Override
public boolean equals(Object obj) {
    if(obj == null)
        return false;
    if(!(obj instanceof Contact)) 
        return false;

    Contact other = (Contact) obj;
    if(! this.name.equalsIgnoreCase(other.name)) return false;

    return true;
}
  }

public class ContactService {

    private Set<Contact> contacts;

    public ContactService() {
        this.contacts =  new TreeSet<>();
    }

    public void addContact(String name) {
        Contact contact = new Contact(name);
        contacts.add(contact);
    }

    public void searchContact(String searchStr) {
        System.out.println(contacts);
        for (Contact contact : contacts) {
            if (contact.getName().equalsIgnoreCase(searchStr)||(searchStr.contains(" ") && contact.getName().contains(searchStr))) {
                System.out.println(contact.getName());
            } else if (contact.getFirstName().toLowerCase().startsWith(searchStr) || contact.getLastName().toLowerCase().startsWith(searchStr)) {
                System.out.println(contact.getName());
            }
        }
    }
}

Please suggest how to improve performance in above code.

Answer 1

You could use a java.util.HashMap , to store a lookup table for Contacts for search terms.

The idea is to pre-populate the lookup table with likely search terms (eg the first name or the first three letters of the name). If your lookup doesn't return any matches you can always perform a full search. If you want more powerful searching you could look at something like Apache Lucene .

Eg

Map<String, Set<Contact>> contactLookup = new HashMap<>();

Then you'd start by looking up the search term in the map. This would narrow down the possibilities to a small set which you can iterate over using the same method you use above.

You might also look at the Multimap from Guava, which provides the same capability more elegantly.

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By the way (on an unrelated note) when you override the compareTo() method it is good practice to also override equals() so that (x.compareTo(y)==0) == (x.equals(y)) .

And when you override equals() you will also need to override hashCode() !

Answer 2

I dont have predefined searchTerms, my requirement is like User entered contacts like "Manoj Pathak", "Manoj". If user type "Man" and hit search then result will be Manoj Pathak Manoj If user type "Manoj" and hit search then result will be Manoj (exact match) Manoj Pathak"

In this case I will suggest you implement Longest prefix matching – A Trie based solution in Java which internally will use HashMap.