哈希表(Java实现)

package com.xz.hashtab;

import java.util.Scanner;


public class HashTabDemo {
    public static void main(String[] args) {
        //创建HashTab
        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("exit: 退出系统");

            key = scanner.next();
            switch (key) {
                case "add":
                    System.out.print("输入id:");
                    int id = scanner.nextInt();
                    System.out.print("输入姓名:");
                    String name = scanner.next();
                    Emp emp = new Emp(id, name);
                    hashTab.add(emp);
                    break;
                case "list":
                    hashTab.list();
                    break;
                case "find":
                    System.out.print("请输入你想要查找的id:");
                    id = scanner.nextInt();
                    hashTab.findEmpById(id);
                    break;
                case "exit":
                    scanner.close();
                    System.exit(0);
                default:
                    break;
            }
        }
    }
}

class HashTab {
    private EmplinkedList[] emplinkedLists;
    int size;

    public HashTab(int size) {
        this.emplinkedLists = new EmplinkedList[size];
        for (int i = 0; i < emplinkedLists.length; i++) {
            emplinkedLists[i] = new EmplinkedList();
        }
        this.size = size;
    }

    //添加雇员
    public void add(Emp emp) {
        //根据员工id,得到该员工应该加到哪条链表
        int emplinkedListNo = hashFun(emp.id);
        emplinkedLists[emplinkedListNo].add(emp);
    }

    //根据输入的id,查找雇员
    public void findEmpById(int id) {
        //使用散列函数确定到哪条链表查找
        int emplinkedListNO = hashFun(id);
        Emp emp = emplinkedLists[emplinkedListNO].findEmpById(id);
        if (emp != null) {//找到
            System.out.println("在第" + (emplinkedListNO + 1) + "条链表中找到 雇员 id = " + id);
        } else {
            System.out.println("在哈希表中，没有找到该雇员~");
        }
    }


    //显示所有链表
    public void list() {
        for (int i = 0; i < emplinkedLists.length; i++) {
            emplinkedLists[i].list(i);
        }
    }

    //散列函数,取模法
    public int hashFun(int id) {
        return id % size;
    }
}

class EmplinkedList {
    Emp head = null;

    //添加雇员
    public void add(Emp emp) {
        //如果是第一个雇员
        if (head == null) {
            head = emp;
            return;
        }
        //如果不是第一个,创建一个指针,帮助找到链表最后
        Emp temp = head;
        while (true) {
            if (temp.next == null) {
                break;
            }
            temp = temp.next;
        }
        temp.next = emp;
    }

    //遍历雇员信息
    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) + "链表的信息为:");
        Emp temp = head;
        while (true) {
            System.out.print("=> id = " + temp.id + " name = " + temp.name);
            if (temp.next == null) {
                break;
            }
            temp = temp.next;//指针后移
        }
        System.out.println();
    }

    //根据id查找雇员
    //如果查找到，就返回Emp, 如果没有找到，就返回null
    public Emp findEmpById(int id) {
        //判断链表是否为空
        if (head == null) {
            System.out.println("链表为空");
            return null;
        }
        //辅助指针
        Emp curEmp = head;
        while (true) {
            if (curEmp.id == id) {//找到
                break;//这时curEmp就指向要查找的雇员
            }
            if (curEmp.next == null) {//说明遍历当前链表没有找到该雇员
                curEmp = null;
                break;
            }
            curEmp = curEmp.next;
        }

        return curEmp;
    }
}

class Emp {
    public int id;
    public String name;
    public Emp next;//next默认为null

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