java中HashSet实现(转)

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：