java - Didnot override hashCode() and equals() methods.But could find my stuff -

according scjp book,if donot override hashcode() , equals() method in class being used part of key our code should run , compile not find out stuff.

did not override hashcode() , equals() method in class used part of key,yet value retrieved.

please find code below:

case 1:

import java.util.hashmap; import java.util.map;  class dog1{       public dog1(){}     public dog1(string n) {         // todo auto-generated constructor stub         name=n;     }     string name; }  public class mapgen {      public static void main(string[] args) {          map<object,object> m = new hashmap<object,object>();         dog1 d1=new dog1("clover");         //dog1 d2 =new dog1("clover");         m.put(d1, "xyz");         system.out.println(""+m.get(d1));         system.out.println(""+m.size());       }  } 

output:

xyz

1

while in following case see unable retrieve value. case 2:

import java.util.hashmap; import java.util.map;  class dog1{       public dog1(){}     public dog1(string n) {         // todo auto-generated constructor stub         name=n;     }     string name; }  public class mapgen {      public static void main(string[] args) {          map<object,object> m = new hashmap<object,object>();         dog1 d1=new dog1("clover");         //dog1 d2 =new dog1("clover");         m.put(new dog1(), "xyz");         system.out.println(""+m.get(new dog1()));         system.out.println(""+m.size());       }  } 

output:

null

1

can explain me difference between case 1 , case 2??

in case 1 searching same dog1 instance inserted, means hashcode() implementation object works fine (in fact, sane implementation work, since using exact same object).

in second case using 2 different instances when inserting , retrieving, doesn't work. object#hashcode() method typically implemented converting internal address of object integer, means 2 instances pretty have different hash codes.