import java.util.*;

public class PrintingContainers {
  static Collection fill(Collection c) {
    c.add("dog");
    c.add("dog");
    c.add("cat");
    return c;
  }
  static Map fill(Map m) {
    m.put("dog", "Bosco");
    m.put("dog", "Spot");
    m.put("cat", "Rags");
    return m;
  }
  public static void main(String[] args) {
    System.out.println(fill(new ArrayList()));
    System.out.println(fill(new HashSet()));
    System.out.println(fill(new HashMap()));
  }
} ///:~


運行結果：
[dog,dog,cat]
[cat,dog]
[cat=Rags, dog=Spot]