1. hashcode custom strings
2. Custom MyHashMap
3. Find content performance compare
Wherein: IHashMap interfaces, Entry following classes
1 package Collection; 2 3 public interface IHashMap { 4 public void put(String key,Object value); 5 public Object get(String key); 6 7 }
1 package Collection; 2 3 public class Entry { 4 public Object key; 5 public Object value; 6 public Entry(Object key,Object value){ //构造方法 7 this.key=key; 8 this.value=value; 9 } 10 public String toString(){ 11 return "[key=" + key + ", value=" + value + "]"; 12 } 13 14 }
给出代码：
1 package Collection; 2 3 import java.util.ArrayList; 4 import java.util.HashSet; 5 import java.util.Iterator; 6 import java.util.LinkedList; 7 import java.util.List; 8 9 import charactor.Hero; 10 11 public class myHashMap implements IHashMap { 12 public static int hashcode(String str) { 13 if (str.length() == 0) 14 return 0; 15 char tmpCharArr[] = str.toCharArray(); 16 int cnt = 0; 17 for (int i = 0; i < tmpCharArr.length; i++) 18 cnt += (int) tmpCharArr[i]; 19 cnt = cnt * 23; 20 if (cnt < 0) 21 cnt = cnt * (-1); 22 if (cnt > 1999) 23 cnt = cnt % 2000; 24 return cnt; 25 26 // //测试hashcode,大小为5 27 // if(str.length()==0) 28 // return 0; 29 // int cnt=Integer.parseInt(str); 30 // if(cnt>=5) 31 // return cnt%5; 32 // return cnt; 33 // 34 } 35 36 public static char ranChar() { 37 while (true) { 38 int n = (int) Math.round(Math.random() * 128); 39 char c = (char) n; 40 if (Character.isDigit(c) || Character.isLetter(c)) 41 return c; 42 } 43 } 44 45 public static List<String> ranArr(int num) { // 随机生成长度是2-10的不等的num个字符串 46 List<String> arr = new ArrayList(); // 最后返回arr 47 HashSet<String> hs = new HashSet(); // 保证随机生成的字符串互不相等 48 int i = 0; 49 while (i < num) { 50 int randLength = (int) (Math.round(Math.random() * 8) + 2);// 随机生成长度是2-10 51 String tmpStr = ""; 52 for (int j = 0; j < randLength; j++) { 53 tmpStr += ranChar(); 54 } 55 if (hs.add(tmpStr) == true) // 保证随机生成的字符串互不相等 56 i++; 57 } 58 for (String s : hs) { // HashSet转成List便于以后的操作 59 arr.add(s); 60 } 61 return arr; 62 } 63 64 Object[] hashArr = new Object[2000]; // 自己定义的Hash表，由2000个对象组成 65 66 @Override 67 public void put(String key, Object value) { 68 // TODO Auto-generated method stub 69 int index = hashcode(key); 70 // 下面两行用于应对hashArr[index]为空时，填入LinkedList<Entry>类型 71 LinkedList<Entry> tmpLinkedList = new LinkedList(); 72 Entry E = new Entry(key, value); 73 tmpLinkedList.add(E); 74 75 if (hashArr[index] == null) { 76 hashArr[index] = tmpLinkedList; 77 } else {// hashArr[index]非空，说明它本身是LinkedList<Entry>类型，直接add即可 78 LinkedList<Entry> ll = (LinkedList<Entry>) hashArr[index]; 79 ll.add(E); 80 } 81 } 82 83 @Override 84 public Object get(String key) { 85 // TODO Auto-generated method stub 86 int index = hashcode(key); 87 if (hashArr[index] == null) 88 return null; 89 else { 90 LinkedList<Entry> tmpList = (LinkedList<Entry>) hashArr[index]; 91 for (int i = 0; i < tmpList.size(); i++) { 92 if (tmpList.get(i).key.equals(key)) { // 找到了对应的key--value 93 return tmpList.get(i).value; // 返回key对应的value 94 } else { 95 return null; 96 } 97 } 98 } 99 return null; 100 } 101 102 public Object get2(String key) { // 用于测试myHashMap性能 103 // TODO Auto-generated method stub 104 int index = hashcode(key); 105 if (hashArr[index] == null) 106 return null; 107 else { 108 LinkedList<Entry> tmpList = (LinkedList<Entry>) hashArr[index]; 109 int cnt = 0;//"hero-5555"的数量 110 //"hero-5555"以外的hero也可能hash到和"hero-5555"相同的地方，只好for循环找出来 111 for (int i = 0; i < tmpList.size(); i++) { 112 if (tmpList.get(i).key.equals(key)) { // 找到了对应的key-value 113 cnt++; 114 } 115 } 116 return cnt; 117 } 118 } 119 public static void testHashCode(){ 120 List<String> rndArr=ranArr(100); 121 List <Integer>rndArrHashCode=new ArrayList(); 122 for(int i=0;i<100;i++){ 123 rndArrHashCode.add(hashcode(rndArr.get(i))); 124 } 125 System.out.println("HashCode后的值为："); 126 System.out.println(rndArrHashCode); 127 } 128 129 public static void testEfficiency(int n) { //n是测试规模 130 ArrayList<Hero> heros = new ArrayList<>(); 131 myHashMap mp = new myHashMap(); 132 for (int i = 0; i < n; i++) { 133 int rnd = (int) Math.round(Math.random() * 9000 + 1000); 134 heros.add(new Hero("hero-" + rnd)); // 办法一 135 mp.put("hero-" + rnd, rnd); // 办法二 136 } 137 138 // 办法一：for循环查找 139 long st1 = System.currentTimeMillis(); 140 int cnt1 = 0; // 统计"hero-5555"个数 141 for (int i = 0; i < n; i++) { 142 if (heros.get(i).name.equals("hero-5555")) 143 cnt1++; 144 } 145 long et1 = System.currentTimeMillis(); 146 System.out.printf("for循环耗时：%d ms\n共找到%d个\n", (et1 - st1), cnt1); 147 148 // 办法二：myHashMap查找 149 150 long st2 = System.currentTimeMillis(); 151 int cnt2 = 0; // 统计"hero-5555"个数 152 cnt2 = (int) mp.get2("hero-5555"); 153 long et2 = System.currentTimeMillis(); 154 System.out.printf("myHashMap耗时：%d ms\n共找到%d个", (et2 - st2), cnt2); 155 } 156 157 public static void main(String[] args) { 158 testHashCode(); 159 testEfficiency(300000); 160 } 161 }
效果图：
