chart11 持有对象

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11.3 添加对象实例：AsListInference.java，

//: holding/AsListInference.java  // Arrays.asList() makes its best guess about type.  import java.util.*;  class Snow {}  class Powder extends Snow {}  class Light extends Powder {}  class Heavy extends Powder {}  class Crusty extends Snow {}  class Slush extends Snow {}  public class AsListInference {      public static void main(String[] args) {          List<Snow> snow1 = Arrays.asList(              new Crusty(), new Slush(), new Powder());          // Won't compile:          // List<Snow> snow2 = Arrays.asList(              // new Light(), new Heavy());          // Compiler says:          // found : java.util.List<Powder>          // required: java.util.List<Snow>          // Collections.addAll() doesn't get confused:          List<Snow> snow3 = new ArrayList<Snow>();          Collections.addAll(snow3, new Light(), new Heavy());          // Give a hint using an          // explicit type argument specification:          List<Snow> snow4 = Arrays.<Snow>asList(              new Light(), new Heavy());      }  } ///:~

解决办法：使用显式类型参数说明（List<Snow> snow4 = Arrays.<Snow>asList(new Light(), new Heavy());），象上面的例子中最后所做的那样。
Collections.addAll()。
public static <T> boolean addAll(Collection<? super T> c, T... elements)该方法接受一个Collection对象，以及一个数组或是一个用逗号分割的列表，将元素添加到Collection中。先构建一个不包含元素的Collection，然后调用Collections.addAll()这种方式很方便，因此是首选方式。
Collection导出类构造器，可以接受另一个Collection，用它来将自身初始化。
Collection的addAll()方法，将指定 collection 中的所有元素都添加到此 collection 中（可选操作）。相比使用构造函数初始化，这种方法快的多。

11.5 当确定一个元素是否属于List（不知这里是否可以换为容器），发现某个元素的索引，以及从某个List中移除一个元素时，都会用到equal（）方法

11.6 迭代器，

Iterater的四个作用

在调用remove()之前，必须先调用next()

“接受对象容器，并传递他，从而在每个对象上都执行操作，这种思想十分强大，并且贯穿于本书”

//: holding/CrossContainerIteration.javaimport typeinfo.pets.*;import java.util.*;public class CrossContainerIteration {  public static void display(Iterator<Pet> it) {    while(it.hasNext()) {      Pet p = it.next();      System.out.print(p.id() + ":" + p + " ");    }    System.out.println();  }  public static void main(String[] args) {    ArrayList<Pet> pets = Pets.arrayList(8);    LinkedList<Pet> petsLL = new LinkedList<Pet>(pets);    HashSet<Pet> petsHS = new HashSet<Pet>(pets);    TreeSet<Pet> petsTS = new TreeSet<Pet>(pets);    display(pets.iterator());    display(petsLL.iterator());    display(petsHS.iterator());    display(petsTS.iterator());  }} /* Output:0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx4:Pug 6:Pug 3:Mutt 1:Manx 5:Cymric 7:Manx 2:Cymric 0:Rat5:Cymric 2:Cymric 7:Manx 1:Manx 3:Mutt 6:Pug 4:Pug 0:Rat*///:~

Iterater,能够将遍历序列的操作与序列的底层的结构分离，迭代器统一对容器的访问形式

listIterater只适用于list类型的访问，不过它能够实现双向的移动

//: holding/ListIteration.javaimport typeinfo.pets.*;import java.util.*;public class ListIteration {  public static void main(String[] args) {    List<Pet> pets = Pets.arrayList(8);    ListIterator<Pet> it = pets.listIterator();    while(it.hasNext())      System.out.print(it.next() + ", " + it.nextIndex() +        ", " + it.previousIndex() + "; ");    System.out.println();    // Backwards:    while(it.hasPrevious())      System.out.print(it.previous().id() + " ");    System.out.println();    System.out.println(pets);    it = pets.listIterator(3);    while(it.hasNext()) {      it.next();      it.set(Pets.randomPet());    }    System.out.println(pets);  }} /* Output:Rat, 1, 0; Manx, 2, 1; Cymric, 3, 2; Mutt, 4, 3; Pug, 5, 4; Cymric, 6, 5; Pug, 7, 6; Manx, 8, 7;7 6 5 4 3 2 1 0[Rat, Manx, Cymric, Mutt, Pug, Cymric, Pug, Manx][Rat, Manx, Cymric, Cymric, Rat, EgyptianMau, Hamster, EgyptianMau]*///:~

11.10 Map可以返回它的键的Set,它的值得Collection,或者他的键值对的Set

linklist 实现了list接口和Queue接口

11.3 迭代器与Foreach

foreach语法可以用于数组和任何的collection容器，一个类如果想用foreach来遍历这个类的对象，那么这个类必须实现Iterater接口，（Demo）

//: holding/IterableClass.java// Anything Iterable works with foreach.import java.util.*;public class IterableClass implements Iterable<String> {  protected String[] words = ("And that is how " +    "we know the Earth to be banana-shaped.").split(" ");  public Iterator<String> iterator() {    return new Iterator<String>() {      private int index = 0;      public boolean hasNext() {        return index < words.length;      }      public String next() { return words[index++]; }      public void remove() { // Not implemented        throw new UnsupportedOperationException();      }    };  }  public static void main(String[] args) {    for(String s : new IterableClass())      System.out.print(s + " ");  }} /* Output:And that is how we know the Earth to be banana-shaped.*///:~

11.13.1 适配器方法惯用法

ModifyingArraysASList.java重要

//: holding/ModifyingArraysAsList.javaimport java.util.*;public class ModifyingArraysAsList {  public static void main(String[] args) {    Random rand = new Random(47);    Integer[] ia = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };    List<Integer> list1 =      new ArrayList<Integer>(Arrays.asList(ia));    System.out.println("Before shuffling: " + list1);    Collections.shuffle(list1, rand);    System.out.println("After shuffling: " + list1);    System.out.println("array: " + Arrays.toString(ia));    List<Integer> list2 = Arrays.asList(ia);    System.out.println("Before shuffling: " + list2);    Collections.shuffle(list2, rand);    System.out.println("After shuffling: " + list2);    System.out.println("array: " + Arrays.toString(ia));  }} /* Output:Before shuffling: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]After shuffling: [4, 6, 3, 1, 8, 7, 2, 5, 10, 9]array: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]Before shuffling: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]After shuffling: [9, 1, 6, 3, 7, 2, 5, 10, 4, 8]array: [9, 1, 6, 3, 7, 2, 5, 10, 4, 8]*///:~

11.14 总结

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