在arrayList中找到一个特定的对象

Question

I have a big arrayList filled with a file ( over 50000 line) and i need to find a specific object in this list

My object class

public class City{

    public City() {
        super();

    }
    private String name;
    private String department;


    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.nom = name;
    }
    public String getDepartment() {
        return deparement;
    }
    public void setDepartment(String department) {
        this.department = department;
    }

    @Override
    public String toString() {

        return name;
    }
}

A solution is doing

List<City> listCity = ParseFile.parseCityFile(this);
String item = textView.getText().toString();
                for (City c : listCity ) {
                    if(c.getName().equals(item))                                    
                        // stuff here
                }

but it's not receivable for obvious performance reasons. Any advices for a better way to do this ?

Answer 1

Use a Map<String, City> instead of List<City> , use the City#name as the key in your map. If navigation order won't matter, then use HashMap as implementation, otherwise use LinkedHashMap or TreeMap .

Answer 2

In your class City override equals() , hashCode() and Comparable -

@Override
public boolean equals(Object b) {
  if (b != null) {
    if (this == b) return true;
    return this.getName().equals(((City) b).getName());
  }
  return false;
}

@Override
public int hashCode() {
  return this.getName().hashCode();
}

@Override
public int compareTo(City o) {
  return this.getName().compareTo(o);
}

Then you can use

if (listCity.contains(item)) {
}

And then for fast look-up you can use a Map, or a TreeSet . A TreeSet (per the Javadoc),

This implementation provides guaranteed log(n) time cost for the basic operations (add, remove and contains).

Answer 3

I'd use equals() method (add it to your City class):

public boolean equals(Object object) {
    boolean areEquals = false;
    if (object instanceof City) {
        City otherCity = (City) object;
        areEquals = (this.getName() == otherCity.getName() && this.getDepartment() == otherCity.getDepartment());
    }
    return areEquals;
}

And I'd also replace your if condition by:

if (listCity.contains(item)) {
}

And that should do the trick!