Search.java

import java.util.Arrays;
import java.util.List;

/**
 * 検索クラス
 */
public class Search {

    private static List<Person> persons = Arrays.asList(
            new Person("Tarou", "Tokyo"),
            new Person("Jirou", "Osaka"),
            new Person("Saburou", "Nagoya"));

    static Person find(String name) {
        for (Person p : Search.persons) {
            if (p.getName().equals(name)) {
                return p;
            }
        }
        return new NullPerson(name);  // null の代わりに Null オブジェクトを返す
    }

    public static void main(String[] args) {
        System.out.println(find("Tarou").getAddress());
        System.out.println(find("Hanako").getAddress());
    }
}

/**
 * 「人」を表わすクラス
 */
class Person {

    private String name;
    private String address;

    Person() {
    }

    Person(String name, String address) {
        this.name = name;
        this.address = address;
    }

    String getName() {
        return this.name;
    }

    String getAddress() {
        return this.address;
    }

    @Override
    public String toString() {
        return this.name + ":" + this.address;
    }
}

/**
 * Null オブジェクト
 */
class NullPerson extends Person {

    NullPerson(String name) {
        super(name, "");
    }

    @Override
    String getAddress() {
        return super.getName() + " ha imasen";
    }
}