博客

一、Set集合

Set 接口 集 ： 数据是唯一存储，无序的。

HashSet实现类：

底层 数据结构 哈希表。

1.HashSet

数组 + 链表 + 二叉树。

原理:

原码:

        /*
         * new HashSet:
         * 加载因子:
         *  static final float DEFAULT_LOAD_FACTOR = 0.75f; 
         *  
         *  数组的初始容量： 16
         *   static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
         *  二叉树节点临界值:
         *  static final int TREEIFY_THRESHOLD = 8;
         *   
         */
        HashSet<String> set = new HashSet<>();
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    p = e;
                }
            }
    }
}
        Set<String> set = new HashSet<>();
        set.add("ab");
        set.add("ac");
        set.add("ba");
        System.out.println(set);// [ab, ac, ba]
        set.add("ab");
        System.out.println(set);// [ab, ac, ba]

重写：hashCode和equals()方法：

class Student{
    private int no;
    private String name;
    public Student(int no, String name) {
        this.no = no;
        this.name = name;
    }
    public int getNo() {
        return no;
    }
    public String getName() {
        return name;
    }
    @Override
    public String toString() {
        return "Student [no=" + no + ", name=" + name + "]";
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + no;
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)// guojing.equals(guojing)
            return true;
        if (obj == null)// guojing.equals(null)
            return false;
        if (this.getClass() != obj.getClass())//  guojing.equals("hello")
            return false;
        Student other = (Student) obj;// 
        if (no != other.no)
            return false;
        return true;
    }
    
/*  @Override
    public int hashCode() {
        return no;
    }
    @Override
    public boolean equals(Object obj) {
        //  只要学号相同 那么 就返回 true
        // this.no    (Student)obj .no
        Student stu = (Student)obj;// 
        return this.no == stu.no;
    }*/
    
}
public class TestHashSet1 {
​
    public static void main(String[] args) {
        Set<Student> set = new HashSet<>();
        Student guojing = new Student(11, "郭靖");
        Student yangkang = new Student(11, "郭靖");
        Student huangrong = new Student(22, "黄蓉");
        set.add(guojing);
        set.add(yangkang);
        set.add(huangrong);

    //信息
        set.forEach(System.out::println);
        
        
​
    }
​}

2、TreeSet

基本应用：

   public static void main(String[] args) {
        // 默认： 自然升序排序 Comparable
//      Set<String> set = new TreeSet<>();
        // Comparator
        Set<String> set = new TreeSet<>((s1,s2)->s2.compareTo(s1));
        set.add("aa");
        set.add("cc");
        set.add("bb");
//      System.out.println(set);// [aa, bb, cc]
        System.out.println(set);// [cc, bb, aa]
​