哈希表的介绍和内存布局
import java.util.Scanner;
public class HashTabTest {
public static void main(String[] args) {
//创建哈希表
HashTab hashTab = new HashTab(10);
//编写运行时提示窗口
String key = "";
Scanner scanner = new Scanner(System.in);
while(true){
System.out.println("输入add: 添加职员");
System.out.println("输入list: 打印所有链表中的职员信息");
System.out.println("输入find: 根据id查找职员");
System.out.println("输入delete: 根据id删除职员");
System.out.println("输入exit: 退出系统");
key = scanner.next();
switch (key){
case "add":
System.out.println("请输入id");
int id = scanner.nextInt();
System.out.println("请输入姓名");
String name = scanner.next();
Emp emp = new Emp(id, name);
hashTab.add(emp);
break;
case "list":
hashTab.list();
break;
case "exit":
System.out.println("程序退出");
scanner.close();
System.exit(0);
case "find":
System.out.println("请输入一个id");
int empid = scanner.nextInt();
hashTab.findEmpById(empid);
break;
case "delete":
System.out.println("请输入一个id");
int empid1 = scanner.nextInt();
hashTab.deleteEmpById(empid1);
break;
default:
System.out.println("请输入正确的操作代码");
break;
}
}
}
}
//节点类
class Emp{
//职员
public int id;
public String name;
public Emp next;
public Emp(int id, String name) {
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "Emp{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}
//链表类
class LinkedList{
private Emp head;
//添加方法, 假设每次新添加的节点都是自增的, 所以都是添加在最后
public void add(Emp emp){
if (head == null){
//如果该链表为空直接添加
head = emp;
return;
}
//辅助指针
Emp cur = head;
while(true){
if (cur.next == null){
break;
}
cur = cur.next;
}
//出这个while之后cur就是最后一个节点
cur.next = emp;
}
//遍历的方法
public void list(int i){
if (head == null){
System.out.println("第"+(i+1)+"条链表为空!");
return;
}
System.out.print("第"+(i+1)+"条链表信息为");
Emp cur = head;
while(true){
System.out.printf("=> id=%d name=%s\t", cur.id, cur.name);
if (cur.next == null){
break;
}
cur = cur.next;
}
System.out.println(); //换行
}
//查找某个id的方法
public Emp findEmpById(int id){
if (head == null){
return null;
}
Emp cur = head;
while(true){
if (cur.id == id){
return cur;
}
if (cur.next == null){
break;
}
cur = cur.next;
}
return null;
}
//删除某个id的职员信息
public void deleteEmp(int id){
if (head == null){
System.out.println("没有这个职员");
return;
}
if (head.id == id){
head = head.next;
System.out.println("删除完成");
return;
}
Emp cur = head;
while(cur.next != null){
if (cur.next.id == id){
cur.next = cur.next.next;
System.out.println("删除完成");
return;
}
cur = cur.next;
}
System.out.println("没有这个职员");
return;
}
}
//创建Hashtab的对象
class HashTab{
private LinkedList[] empHashTab;
int size;
//初始化
public HashTab(int size) {
this.size = size;
empHashTab = new LinkedList[size];
for (int i=0; i < size; i++){
empHashTab[i] = new LinkedList();
}
}
//编写散列函数: 根据emp的id确定往哪条链表添加
public int sanlie(int id){
return id % size;
}
//添加方法
public void add(Emp emp){
//得到下标
int linkedlistno = sanlie(emp.id);
empHashTab[linkedlistno].add(emp);
}
//遍历整个哈希表
public void list(){
for (int i=0; i<size; i++){
empHashTab[i].list(i);
}
}
//查找某个id的职员信息
public void findEmpById(int id){
int linkedlistno = sanlie(id);
Emp empById = empHashTab[linkedlistno].findEmpById(id);
if (empById == null){
System.out.println("没有id为"+id+"的职员");
return;
}else{
System.out.println("id为"+id+"的职员信息为"+empById);
}
}
//删除
public void deleteEmpById(int id){
int linkedlistno = sanlie(id);
empHashTab[linkedlistno].deleteEmp(id);
}
}