哈希表

哈希表是一种数据结构，它提供了快速的插入操作和查找操作。其基于数组来实现。

    /**  
     * 员工信息类  
     * @author Administrator  
     *  
     */   
    public class Info {   
        private String key;   
        private String name;   
       
        public Info(String key, String name) {   
            this.key = key;   
            this.name = name;   
        }   
       
        public String getKey() {   
            return key;   
        }   
       
        public void setKey(String key) {   
            this.key = key;   
        }   
       
        public String getName() {   
            return name;   
        }   
       
        public void setName(String name) {   
            this.name = name;   
        }   
    }  

    import java.math.BigInteger;   
       
    public class HashTable {   
        private Info[] arr;   
       
        /**  
         * 默认的构造方法  
         */   
        public HashTable() {   
            arr = new Info[100];   
        }   
       
        /**  
         * 指定数组初始化大小  
         */   
        public HashTable(int maxSize) {   
            arr = new Info[maxSize];   
        }   

    public class TestHashTable {   
        public static void main(String[] args) {   
            HashTable ht = new HashTable();   
            ht.insert(new Info("a","张三"));   
            ht.insert(new Info("ct","李四"));   
            ht.insert(new Info("wangwu","王五"));   
       
            System.out.println(ht.find("a").getName());   
            System.out.println(ht.find("ct").getName());   
        }   
    }   

        /**  
         * 插入数据  
         */   
        public void insert(Info info) {   
            arr[hashCode(info.getKey())] = info;   
        }   
       
        /**  
         * 查找数据  
         */   
        public Info find(String key) {   
            return arr[hashCode(key)];   
        }   
       
        public int hashCode(String key) {   
    //      int hashVal = 0;   
    //      for(int i = key.length() - 1; i >= 0; i--) {   
    //          int letter = key.charAt(i) - 96;   
    //          hashVal += letter;   
    //      }   
    //      return hashVal;   
       
            BigInteger hashVal = new BigInteger("0");   
            BigInteger pow27 = new BigInteger("1");   
            for(int i = key.length() - 1; i >= 0; i--) {   
                int letter = key.charAt(i) - 96;   
                BigInteger letterB = new BigInteger(String.valueOf(letter));   
                hashVal = hashVal.add(letterB.multiply(pow27));   
                pow27 = pow27.multiply(new BigInteger(String.valueOf(27)));   
            }   
            return hashVal.mod(new BigInteger(String.valueOf(arr.length))).intValue();   
        }   
    }