概述?

Set也是集合Collection接口的子接口

Set也是集合Collection接口的子接口

特點：不保證元素有順序，數(shù)組元素不可以重復(fù)

HashSet:

底層是基于HashMap的。元素是無序的。元素不可重復(fù)，去重機制是依據(jù)hashCode()和equals()方法

LinkedHashSet:

元素有序，元素不可重復(fù)，去重機制是依據(jù)hashCode()和equals()

TreeSet:

在底層會對元素進行排序，默認是升序排順，要求存儲在TreeSet集中的元素必須實現(xiàn)Comparable接口，元素不可重復(fù),去重機制是依據(jù)compareTo方法，如果compareTo()方法返回結(jié)果為0，則認為重復(fù)

Deque<String> d= new LinkedList<>();

d.offer("1"); //尾部插入
d.offerFirst("s");//隊首插入
d.offerLast("2"); //隊尾插入
d.poll(); //默認從隊首取值，刪除
d.pollFirst();//從隊首取，并刪除
d.pollLast();//從隊尾取，刪除
d.peek();//從隊首取不刪除
d.peekFirst();
d.peekLast();
d.getFirst();
d.getLast();

Set s = new HashSet();

Student a = new Student("re", 21, 12, "中國");
Student b = new Student("rk", 31, 56, "🚹");
Student c = new Student("ee", 41, 34, "?");
Student d = new Student("qq", 71, 35, "🐷");
Student e = new Student("qq", 71, 35, "🐷");
s.add(a);
s.add(b);
s.add(c);
s.add(d);
s.add(e);

Set s = new LinkedHashSet();

Student a = new Student("re", 21, 12, "中國");
Student b = new Student("rk", 31, 56, "🚹");
Student c = new Student("ee", 41, 34, "?");
Student d = new Student("qq", 71, 35, "🐷");
s.add(a);
s.add(b);
s.add(c);
s.add(d);

Queue<String> queue = new LinkedList<>();

??????? queue.add("1");queue.add("2");queue.add("3");queue.poll();queue.peek();queue.size();queue.forEach(s -> System.out.println(s));Collection<String> c = new ArrayList();
//        Collections.replaceAll(queue,"1","2");System.out.println(queue);
//        queue.removeAll(queue);
//        System.out.println(queue);

? Set<String> s = new HashSet();

 s.add("one");s.add("two");s.add("three");s.add("four");
//        System.out.println("one".hashCode());
//        System.out.println(s);  String[] s11 = s.toArray(new String[s.size()]);
//toArray方法接收一個空的數(shù)組作為參數(shù)，大小等于集合的大小，然后將集合中的元素復(fù)制到這個數(shù)組中并返回該數(shù)組。for (int i = 0; i < s.size(); i++) {System.out.print(s11[i]);}System.out.println(Arrays.toString(s11));Set s1 = new LinkedHashSet();s1.add("one");s1.add("two");s1.add("three");s1.add("four");

?

?

Set s = new TreeSet();

Student a = new Student("re", 21, 12, "中國");

Student b = new Student("rk", 31, 56, "🚹");

Student c = new Student("ee", 41, 34, "?");

Student d = new Student("qq", 71, 35, "🐷");

s.add(a);

s.add(b);

s.add(c);

s.add(d);

System.out.println(s);