java中HashSet实现

hashset底层的数据结构是hash表，hash表实现方式采用数组+链表，数组类型为HashNode，每个数组元素为链表的头指针，链表中存储经过hash函数散列后冲突的元素，数组的长度为26

hashset存储的元素类型为字符串，取每个字符串的首字符的ascall码作为hash函数的输入，数组的长度为10，散列函数h(x)=x%10。

HashNode代码如下：

public class HashNode {private String msg;private HashNode next;public String getMsg() {return msg;}public void setMsg(String msg) {this.msg = msg;}public HashNode getNext() {return next;}public void setNext(HashNode next) {this.next = next;}public HashNode(String msg, HashNode next) {this.msg = msg;this.next = next;}public HashNode() {}}

hashset实现如下：

public class MyHashSet {private HashNode[] nodes = new HashNode[10];private int size = 0;public MyHashSet() {for (int i = 0; i < nodes.length; i++) {nodes[i] = new HashNode();}}public boolean add(String value) {if (contains(value)) { // 如果有这个元素，就不插入return false;}HashNode node = new HashNode(value, null);int index = (int) value.charAt(0) % nodes.length; // 取第一个字符作为hash函数的输入// 如果该链为空，直接插入，否则采用头插法if (nodes[index].getNext() == null) {nodes[index].setNext(node);} else {node.setNext(nodes[index].getNext());nodes[index].setNext(node);}size++;return true;}public boolean remove(String value) {if (!contains(value)) {return false;}int index = (int) value.charAt(0) % nodes.length;HashNode node = nodes[index];HashNode node2 = node.getNext();while (node2 != null) {if (node2.getMsg().equals(value)) {node.setNext(node2.getNext());size--;break;}node = node.getNext();node2 = node.getNext();}return true;}public void display() {for (int i = 0; i < nodes.length; i++) {HashNode node = nodes[i].getNext();System.out.print(i + " :");while (node != null) {System.out.print(node.getMsg() + "  ");node = node.getNext();}System.out.println();}}public int size() {return size;}public boolean contains(String value) {int index = (int) value.charAt(0) % nodes.length;HashNode node = nodes[index].getNext();while (node != null) {if (node.getMsg().equals(value)) {return true;}node = node.getNext();}return false;}}

测试代码：

public class TestMyHashSet {public static void main(String[] args) {MyHashSet myHashSet = new MyHashSet();myHashSet.add("hello");myHashSet.add("hey");myHashSet.add("apply");myHashSet.add("你好");myHashSet.add("你是谁");myHashSet.add("cat");myHashSet.add("dog");myHashSet.add("cat");myHashSet.add("你好");System.out.println("包含'你好'? " + myHashSet.contains("你好"));System.out.println("元素个数: " + myHashSet.size());myHashSet.display();myHashSet.remove("hello");System.out.println("*****************after remove 'hello'**********************");myHashSet.display();System.out.println("元素个数: " + myHashSet.size());}}

输出结果：