哈希表代码实现

哈希表相当于数组+链表

定义员工类

class Emp {
    public int id;
    public String name;
    public Emp next;

    public Emp(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }
}

定义链表类

class EmpLinkedList {
    //头指针，第一个指向的就是雇工
    private Emp head;

    //添加雇工
    public void add(Emp emp) {
        if (head == null) {
            head = emp;
            return;//报错原因
        }
        //如果不是第一个
        Emp cur = head;
        while (true) {
            if (cur.next == null) {
                break;
            }
            cur = cur.next;
        }
        cur.next = emp;
    }

    //遍历链表员工信息
    public void list(int no) {
        if (head == null) {
            System.out.println("第" + (no + 1) + "条链表为空！");
            return;
        }
        System.out.print("第" + (no + 1) + "条链表的信息为：");
        Emp cur = head;
        while (cur != null) {
            System.out.printf("=> id=%d name=%s\t", cur.id, cur.name);
//            if (cur.next == null) {//表示当前是最后一个员工
//                break;
//            }
            cur = cur.next;
        }
        System.out.println();
    }

    //根据id查找员工
    public Emp getById(int id) {
        if (head == null) {
            return null;
        }
        Emp cur = head;
        while (true) {
            if (cur.id == id) {
                break;//查找到员工
            }
            if (cur.next == null) {
                cur = null;
                break;
            }
            cur = cur.next;
        }
        return cur;
    }

    //根据id删除员工
    public void deleteById(int id) {
        if (head == null) {
            return;
        }
        Emp cur = head;
        if (head.id==id){//删除的是第1个员工
            head=head.next;
            return;
        }
        while (true) {
            if (cur.next.id == id) {//删除的是中间的员工，就把当前节点指向下一个的节点
                cur.next=cur.next.next;
            }
            cur = cur.next;
            if (cur==null||cur.next == null) {
                return;
            }
        }
    }
}

定义哈希表

class HashTab {
    private EmpLinkedList[] empLinkedListArray;
    private int size;//表示有多少条链表

    public HashTab(int size) {
        this.size = size;
        empLinkedListArray = new EmpLinkedList[size];
        //这时不要忘了分别初始化每个链表（牢记）
        for (int i = 0; i < size; i++) {
            empLinkedListArray[i] = new EmpLinkedList();
        }
    }

    //添加雇员
    public void add(Emp emp) {
        //根据员工的id添加到对应的链表
        int empLinkedListNO = hashFun(emp.id);
        empLinkedListArray[empLinkedListNO].add(emp);//不初始化，会导致空指针异常
    }

    //遍历所有链表
    public void list() {
        for (int i = 0; i < size; i++) {
            empLinkedListArray[i].list(i);
        }
    }

    //根据id查找emp
    public void findEmpById(int id) {
        //使用散列函数查找哪条链表
        int empLinkedListNO = hashFun(id);
        Emp emp = empLinkedListArray[empLinkedListNO].getById(id);
        if (emp != null) {
            System.out.printf("在第%d条链表找到员工id = %d\n", empLinkedListNO + 1, id);
        } else {
            System.out.println("在哈希表中，没有找到该员工id");
        }
    }

    //根据id删除emp
    public void deleteEmpById(int id){
        //使用散列函数查找哪条链表
        int empLinkedListNO = hashFun(id);
        empLinkedListArray[empLinkedListNO].deleteById(id);
    }

    //编写散列函数，使用简单取模法
    private int hashFun(int id) {
        return id % size;
    }
}

主方法上书写一个菜单来实现功能

public class HashTabDemo {
    public static void main(String[] args) {
        //创建哈希链表
        HashTab hashTab = new HashTab(7);
        //写一个简单的菜单
        String key = "";
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("add:   添加雇员");
            System.out.println("list:  显示雇员");
            System.out.println("find:  查找雇员");
            System.out.println("delete:删除雇员");
            System.out.println("exit:  退出系统");
            key = scanner.next();
            switch (key) {
                case "add":
                    System.out.println("请输入员工id");
                    int id = scanner.nextInt();
                    System.out.println("请输入员工名字：");
                    String name = scanner.next();
                    //创建雇员
                    Emp emp = new Emp(id, name);
                    hashTab.add(emp);
                    break;
                case "list":
                    hashTab.list();
                    break;
                case "find":
                    System.out.println("请输入员工id");
                    id = scanner.nextInt();
                    hashTab.findEmpById(id);
                    break;
                case "delete":
                    System.out.println("请输入员工id");
                    id = scanner.nextInt();
                    hashTab.deleteEmpById(id);
                    break;
                case "exit":
                    scanner.close();
                    System.exit(0);
                default:
                    break;
            }
        }
    }
}