Java编程思想——第十一章续

这一章主要要记住各个对象的方法，至少理解明白用途：

List：一些方法如下

List<Pet> pets = Pets.arrayList(7);

pets.add(h); // Automatically resizes

print("3: " + pets.contains(h));

pets.remove(h); // Remove by object

Pet p = pets.get(2);

print("5: " + pets.indexOf(cymric));

print("6: " + pets.remove(cymric));

print("8: " + pets);

pets.add(3, new Mouse()); // Insert at an index

List<Pet> sub = pets.subList(1, 4);

print("10: " + pets.containsAll(sub));

Collections.sort(sub); // In-place sort

print("11: " + pets.containsAll(sub));

Collections.shuffle(sub, rand); // Mix it up

print("12: " + pets.containsAll(sub));

List<Pet> copy = new ArrayList<Pet>(pets);

sub = Arrays.asList(pets.get(1), pets.get(4));

copy.retainAll(sub);

copy = new ArrayList<Pet>(pets); // Get a fresh copy

copy.remove(2); // Remove by index

copy.removeAll(sub); // Only removes exact objects

copy.set(1, new Mouse()); // Replace an element

copy.addAll(2, sub); // Insert a list in the middle

pets.clear(); // Remove all elements

print("20: " + pets.isEmpty());

pets.addAll(Pets.arrayList(4));

Object[] o = pets.toArray();

Pet[] pa = pets.toArray(new Pet[0]);

print("23: " + pa[3].id());

迭代器Iteraor：可以遍历并选择序列中的对象，客户端程序员不必知道或关心该序列底层的结构的一个对象。迭代器是一个对象！迭代器统一了对容器的访问方式。

1、使用方法Iterator要求容器返回一个Iterator

2、使用next()获得序列中的对象

3、使用hasNext()检查序列中是否还有元素

4、使用remove()将迭代器新近返回的元素删除

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());

}

LisrIterator：Iterator的子类型。ListIterator可以双向移动，可以产生前一个元素和后一个元素的索引。可以用set()方法替换它访问过的最后一个元素。可以调用ListIterator()产生一个指向List开始的一个ListIterator，ListIterator(n)开始指向第n个的元素的ListIterator。

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]

*///:~

LinkedList：插入移除比ArrayList高效，随机访问慢。LinkedList有使用栈队列和双端队列的方法。

public class LinkedListFeatures {

    public static void main(String[] args) {

        LinkedList<Pet> pets =

            new LinkedList<Pet>(Pets.arrayList(5));

        print(pets);

        // Identical:

        print("pets.getFirst(): " + pets.getFirst());

        print("pets.element(): " + pets.element());

        // Only differs in empty-list behavior:

        print("pets.peek(): " + pets.peek());

        // Identical; remove and return the first element:

        print("pets.remove(): " + pets.remove());

        print("pets.removeFirst(): " + pets.removeFirst());

        // Only differs in empty-list behavior:

        print("pets.poll(): " + pets.poll());

        print(pets);

        pets.addFirst(new Rat());

        print("After addFirst(): " + pets);

        pets.offer(Pets.randomPet());

        print("After offer(): " + pets);

        pets.add(Pets.randomPet());

        print("After add(): " + pets);

        pets.addLast(new Hamster());

        print("After addLast(): " + pets);

        print("pets.removeLast(): " + pets.removeLast());

    }

} /* Output:

[Rat, Manx, Cymric, Mutt, Pug]

pets.getFirst(): Rat

pets.element(): Rat

pets.peek(): Rat

pets.remove(): Rat

pets.removeFirst(): Manx

pets.poll(): Cymric

[Mutt, Pug]

After addFirst(): [Rat, Mutt, Pug]

After offer(): [Rat, Mutt, Pug, Cymric]

After add(): [Rat, Mutt, Pug, Cymric, Pug]

After addLast(): [Rat, Mutt, Pug, Cymric, Pug, Hamster]

pets.removeLast(): Hamster

*///:~

Stack：栈方法

class Stack<T> {

    private LinkedList<T> storage = new LinkedList<T>();

    public void push(T v) { storage.addFirst(v); }

    public T peek() { return storage.getFirst(); }

    public T pop() { return storage.removeFirst(); }

    public boolean empty() { return storage.isEmpty(); }

    public String toString() { return storage.toString(); }

}

public class StackTest {

    public static void main(String[] args) {

        Stack<String> stack = new Stack<String>();

        for(String s : "My dog has fleas".split(" "))

            stack.push(s);

        while(!stack.empty())

            System.out.print(stack.pop() + " ");

    }

} /* Output:

fleas has dog My

*/

Set：不保存重复元素。Set与Colllection具有完全一样的接口，只是行为不同。

public class SetOperations {

    public static void main(String[] args) {

        Set<String> set1 = new HashSet<String>();

        Collections.addAll(set1, "A B C D E F G H I J K L".split(" "));

        set1.add("M");

        System.out.println("H: " + set1.contains("H"));

        System.out.println("N: " + set1.contains("N"));

        Set<String> set2 = new HashSet<String>();

        Collections.addAll(set2, "H I J K L".split(" "));

        System.out.println("set2 in set1: " + set1.containsAll(set2));

        set1.remove("H");

        System.out.println("set1: " + set1);

        System.out.println("set2 in set1: " + set1.containsAll(set2));

        set1.removeAll(set2);

        System.out.println("set2 removed from set1: " + set1);

        Collections.addAll(set1, "X Y Z".split(" "));

        System.out.println("'X Y Z' added to set1: " + set1);

    }

} /*

 * Output: H: true N: false set2 in set1: true set1: [D, K, C, B, L, G, I, M, A,

 * F, J, E] set2 in set1: false set2 removed from set1: [D, C, B, G, M, A, F, E]

 * 'X Y Z' added to set1: [Z, D, C, B, G, M, A, F, Y, X, E]

 */// :~

Map：对象对象映射起来。

public class MapOfList {

    public static Map<Person, List<? extends Pet>> petPeople = new HashMap<Person, List<? extends Pet>>();

    static {

        petPeople.put(new Person("Dawn"),

                Arrays.asList(new Cymric("Molly"), new Mutt("Spot")));

        petPeople.put(new Person("Kate"), Arrays.asList(new Cat("Shackleton"),

                new Cat("Elsie May"), new Dog("Margrett")));

        petPeople.put(new Person("Marilyn"), Arrays.asList(new Pug(

                "Louie aka Louis Snorkelstein Dupree"), new Cat(

                "Stanford aka Stinky el Negro"), new Cat("Pinkola")));

        petPeople.put(new Person("Luke"),

                Arrays.asList(new Rat("Fuzzy"), new Rat("Fizzy")));

        petPeople.put(new Person("Isaac"), Arrays.asList(new Rat("Freckly")));

    }

    public static void main(String[] args) {

        print("People: " + petPeople.keySet());

        print("Pets: " + petPeople.values());

        for (Person person : petPeople.keySet()) {

            print(person + " has:");

            for (Pet pet : petPeople.get(person))

                print(" " + pet);

        }

    }

} /*

 * Output: People: [Person Luke, Person Marilyn, Person Isaac, Person Dawn,

 * Person Kate] Pets: [[Rat Fuzzy, Rat Fizzy], [Pug Louie aka Louis Snorkelstein

 * Dupree, Cat Stanford aka Stinky el Negro, Cat Pinkola], [Rat Freckly],

 * [Cymric Molly, Mutt Spot], [Cat Shackleton, Cat Elsie May, Dog Margrett]]

 * Person Luke has: Rat Fuzzy Rat Fizzy Person Marilyn has: Pug Louie aka Louis

 * Snorkelstein Dupree Cat Stanford aka Stinky el Negro Cat Pinkola Person Isaac

 * has: Rat Freckly Person Dawn has: Cymric Molly Mutt Spot Person Kate has: Cat

 * Shackleton Cat Elsie May Dog Margrett

 */// :~