day34 Set

概述

Set也是集合Collection接口的子接口

特点：不保证元素有顺序，数组元素不可以重复

HashSet:

底层是基于HashMap的。元素是无序的。元素不可重复，去重机制是依据hashCode()和equals()方法

LinkedHashSet:

元素有序，元素不可重复，去重机制是依据hashCode()和equals()

TreeSet:

在底层会对元素进行排序，默认是升序排顺，要求存储在TreeSet集中的元素必须实现Comparable接口，元素不可重复,去重机制是依据compareTo方法，如果compareTo()方法返回结果为0，则认为重复

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

d.offer("1"); //尾部插入
d.offerFirst("s");//队首插入
d.offerLast("2"); //队尾插入
d.poll(); //默认从队首取值，删除
d.pollFirst();//从队首取，并删除
d.pollLast();//从队尾取，删除
d.peek();//从队首取不删除
d.peekFirst();
d.peekLast();
d.getFirst();
d.getLast();

Set s = new HashSet();

Student a = new Student("re", 21, 12, "中国");
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, "中国");
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方法接收一个空的数组作为参数，大小等于集合的大小，然后将集合中的元素复制到这个数组中并返回该数组。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, "中国");

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);