Hash table to achieve the basic principles and methods (Java)

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Basic introduction hash table:

Hash table (Hash table, also called a hash table), based on the key code value (Key value) to directly access a data structure. In other words, to access the records by key values are mapped to table a position to speed up the search. This mapping function called a hash function, recording storage array is called a hash table.
The logic diagram is shown below:

Presentation topics:

There is a company, when a new employee to report, require employees to join the information (id, gender, age, address ...), when the input id of the employee is required to find all information about the employee.

Requirements: do not use a database to try to save memory, the faster the better => hash table (hash)

analysis:

To pass the hash table to store employee information, we will have to define three classes (class employee, based list, a hash table class), then the employee defined in the class corresponding lookup, increased traversal methods.

Code structure:

Code:

package HashTable;

import java.util.Scanner;

public class HashTableDemo {

	public static void main(String[] args) {
		HashTab hashtab = new HashTab(7);
		String key = "";
		Scanner sr = new Scanner(System.in);
		while (true) {
			System.out.println("add:增加雇员，list：显示雇员，find:查找雇员，exit：退出");
			key = sr.next();
			switch (key) {
			case "add":
				System.out.println("请输入雇员id：");
				int id = sr.nextInt();
				System.out.println("请输入雇员name：");
				String name = sr.next();
				Emp emp = new Emp(id, name);
				hashtab.add(emp);
				break;
			case "list":
				hashtab.list();
				break;
			case "find":
				System.out.println("请输入要查找雇员的id：");
				int findId = sr.nextInt();
				hashtab.findEmpById(findId);
				break;

			case "exit":
				sr.close();
				System.exit(0);
				break;
			default:
				break;
			}
		}
	}

}

//创建一个哈希表
class HashTab {
	private EmpLinkedList[] empLinkedList;
	private int size;

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

	// 根据员工的id得到应该添加到哪条链表
	public void add(Emp emp) {
		// 得到emp对应的链表
		int EmpLinkedListNum = hashFun(emp.id);
		empLinkedList[EmpLinkedListNum].add(emp);
	}

	// 编写散列函数
	public int hashFun(int id) {
		return id % size;
	}

	// 遍历hashTab
	public void list() {
		for (int i = 0; i < size; i++) {
			empLinkedList[i].list(i);
		}
	}

	// 根据id查找在哈希表中对应的链表
	public void findEmpById(int id) {
		int EmpLinkedListNum = hashFun(id);
		Emp emp = empLinkedList[EmpLinkedListNum].findEmpById(id);
		if (emp == null) {
			System.out.println("在链表中为找到该节点\n");
		} else {
			System.out.printf("id为%d的员工在第%d条链表中\n", id, EmpLinkedListNum + 1);
		}
	}
}

//创建雇员信息
class Emp {
	public int id;
	public String name;
	public Emp next = null;

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

class EmpLinkedList {
	private Emp head;// 定义一个头指针指向链表的第一个元素
	// 创建一个方法将emp加入到链表中

	public void add(Emp emp) {
		if (head == null) {// 链表中第一个节点为空
			head = emp;
			return;
		}
		Emp curEmp = head;// 创建一个辅助节点，因为head不能变化
		while (true) {
			if (curEmp.next == null) {// 找到链表的最后
				break;
			}
			curEmp = curEmp.next;// 将指针curEmp后移
		}
		curEmp.next = emp;// 将emp加入链表

	}

	// 遍历链表
	public void list(int no) {
		if (head == null) {
			System.out.printf("链表%d为空\n", no + 1);
			return;
		}
		System.out.printf("第%d条链表信息为：", no + 1);
		Emp curEmp = head;// 辅助指针
		while (true) {
			System.out.printf("==>id=%d name = %s\t", curEmp.id, curEmp.name);
			if (curEmp.next == null) {// 到链表最后
				break;
			}
			curEmp = curEmp.next;// 后移
		}
		System.out.println();
	}

	public Emp findEmpById(int id) {
		if (head == null) {
			System.out.println("链表为空");
			return null;
		}
		Emp curEmp = head;
		while (true) {
			if (curEmp.id == id) {// 找到要查找的节点
				break;
			}
			if (curEmp.next == null) {
				curEmp = null;
				break;
			}
			curEmp = curEmp.next;
		}
		return curEmp;
	}
}