Collection<Integer> collection =
      new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
    Integer[] moreInts = { 6, 7, 8, 9, 10 };
    collection.addAll(Arrays.asList(moreInts));
    // Runs significantly faster, but you can't
    // construct a Collection this way:
    Collections.addAll(collection, 11, 12, 13, 14, 15);
    Collections.addAll(collection, moreInts);
    // Produces a list "backed by" an array:
    List<Integer> list = Arrays.asList(16,17,18,19,20);
    list.set(1, 99); // OK -- modify an element

键和值保存在 HashMap 中的顺序不是插入顺序，因为 HashMap 实现使用了非常快速的算法来控制顺序。 TreeMap 通过比较结果的升序来保存键， LinkedHashMap 在保持 HashMap 查找速度的同时按键的插入顺序保存键。

// collections/PrintingCollections.java
// Collections print themselves automatically
import java.util.*;

public class PrintingCollections {
  static Collection
  fill(Collection<String> collection) {
    collection.add("rat");
    collection.add("cat");
    collection.add("dog");
    collection.add("dog");
    return collection;
  }
  static Map fill(Map<String, String> map) {
    map.put("rat", "Fuzzy");
    map.put("cat", "Rags");
    map.put("dog", "Bosco");
    map.put("dog", "Spot");
    return map;
  }
  public static void main(String[] args) {
    System.out.println(fill(new ArrayList<>()));
    System.out.println(fill(new LinkedList<>()));
    System.out.println(fill(new HashSet<>()));
    System.out.println(fill(new TreeSet<>()));
    System.out.println(fill(new LinkedHashSet<>()));
    System.out.println(fill(new HashMap<>()));
    System.out.println(fill(new TreeMap<>()));
    System.out.println(fill(new LinkedHashMap<>()));
  }
}
/* Output:
[rat, cat, dog, dog]
[rat, cat, dog, dog]
[rat, cat, dog]
[cat, dog, rat]
[rat, cat, dog]
{rat=Fuzzy, cat=Rags, dog=Spot}
{cat=Rags, dog=Spot, rat=Fuzzy}
{rat=Fuzzy, cat=Rags, dog=Spot}
*/