第11章 持有对象

set不重复：

package main.chapter11;

import java.util.*;

/**
 * p219
 *
 * @author
 * @create 2019-04-17 上午12:09
 **/
public class SimpleCollection {
    public static void main(String[] args){
        Collection<Integer> c = new ArrayList<Integer>();
        Collection<Integer> b = new HashSet<>();

        for (int i=0;i<10;i++){
            b.add(i);
            b.add(i);
        }


        System.out.println(b.size());

        for (Integer s :
                b) {
            System.out.println(s);
        }

    }
}
//执行结果：0到9

Arrays.asList()的用法，1可变参数、2数组
Collections.addAll的用法
list不可add扩展

package main.chapter11;

import java.util.*;

/**
 * p220
 *
 * @author
 * @create 2019-04-17 上午12:26
 **/
public class AddingGroups {
    public static void main(String[] args){

        Collection<Integer> collection = new ArrayList<>(Arrays.asList(1,2,3,4,5));

        Integer[] moreInts = {6,7,8,9,10};

        collection.addAll(Arrays.asList(moreInts));

        Collections.addAll(collection,11,12,13,14,15);

        Collections.addAll(collection,moreInts);

        List<Integer> list = Arrays.asList(16,17,18,19);
        list.set(1,100);

//        list.add(101);

        for (Integer i :
                list) {
            System.out.println(i);
        }

        System.out.println("=======================");

        for (Integer i:
             collection) {
            System.out.println(i);

        }

    }
}

练习4

package main.chapter11;

import java.util.*;

/**
 * ex4,page223
 *
 * @author
 * @create 2019-04-17 上午12:46
 **/
public class GenerateCollection {


    public static String[] movies = new String[]{"11","42","33"};

    public static int index = 0;

    public static Collection next(Collection<String> collection){

        int trueIndex = index%movies.length;
        collection.add(movies[trueIndex]);
        index++;
        return collection;
    }


    public static void main(String[] args){
        for (int i =0;i<10;i++){

            System.out.println("ArrayList" + GenerateCollection.next(new ArrayList<String>()));
            System.out.println("LinkedList" + GenerateCollection.next(new LinkedList<String>()));
            System.out.println("HashSet" + GenerateCollection.next(new HashSet<String>()));
            System.out.println("LinkedHashSet" + GenerateCollection.next(new LinkedHashSet<String>()));
            System.out.println("TreeSet" + GenerateCollection.next(new TreeSet<String>()));
        }
    }
}

List各方法

package main.chapter11;

import java.util.*;

/**
 * p223
 *
 * @author
 * @create 2019-04-17 上午1:27
 **/
public class ListFeatures {

    public static void main(String[] args){
        List<String> pets = new ArrayList<>();

        pets.add("dog");
        pets.add("cat");
        pets.add("fish");
        pets.add("duck");
        pets.add("bear");


        System.out.println("2" + pets);

        pets.remove("dog");

        System.out.println("3" + pets);

        pets.add(2,"dragon");
        System.out.println("4" + pets);

        List<String> sub = pets.subList(2,5);
        System.out.println("5" + sub);

        Collections.sort(sub);
        System.out.println("6" + sub);

        Collections.shuffle(sub,new Random(33));
        System.out.println("7" + sub);

        List<String> copy = new ArrayList<>(pets);
        sub = Arrays.asList(sub.get(1),sub.get(2));
        System.out.println("8" + sub);

        //交集
        copy.retainAll(sub);
        System.out.println("9" + copy);

        copy = new ArrayList<>(pets);
        copy.removeAll(sub);
        System.out.println("10" + copy);

        copy.addAll(2,sub);
        System.out.println("11" + copy);

        Object[] s = copy.toArray();
        System.out.println("12" + s[0]);

        String[] ss = copy.toArray(new String[0]);
        System.out.println("13" + ss[0]);

    }
}