// equalshashcode/CountedString.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Creating a good hashCode()
import java.util.*;

public class CountedString {
 private static List<String> created =
 new ArrayList<>();
 private String s;
 private int id = 0;
 public CountedString(String str) {
 s = str;
 created.add(s);
 // id is the total number of instances
 // of this String used by CountedString:
 for(String s2 : created)
 if(s2.equals(s))
 id++;
 }
 @Override
 public String toString() {
 return "String: " + s + " id: " + id +
 " hashCode(): " + hashCode();
 }
 @Override
 public int hashCode() {
 // The very simple approach:
 // return s.hashCode() * id;
 // Using Joshua Bloch's recipe:
 int result = 17;
 result = 37 * result + s.hashCode();
 result = 37 * result + id;
 return result;
 }
 @Override
 public boolean equals(Object o) {
 return o instanceof CountedString &&
 Objects.equals(s, ((CountedString)o).s) &&
 Objects.equals(id, ((CountedString)o).id);
 }
 public static void main(String[] args) {
 Map<CountedString,Integer> map = new HashMap<>();
 CountedString[] cs = new CountedString[5];
 for(int i = 0; i < cs.length; i++) {
 cs[i] = new CountedString("hi");
 map.put(cs[i], i); // Autobox int to Integer
 }
 System.out.println(map);
 for(CountedString cstring : cs) {
 System.out.println("Looking up " + cstring);
 System.out.println(map.get(cstring));
 }
 }
}
/* Output:
{String: hi id: 4 hashCode(): 146450=3, String: hi id:
5 hashCode(): 146451=4, String: hi id: 2 hashCode():
146448=1, String: hi id: 3 hashCode(): 146449=2,
String: hi id: 1 hashCode(): 146447=0}
Looking up String: hi id: 1 hashCode(): 146447
0
Looking up String: hi id: 2 hashCode(): 146448
1
Looking up String: hi id: 3 hashCode(): 146449
2
Looking up String: hi id: 4 hashCode(): 146450
3
Looking up String: hi id: 5 hashCode(): 146451
4
*/