hashCode() and equals() - How it is possible

[Sandeep Vaid]

In K&B at page 563 :
"Remember that when you use a class that implements Map, any classes that you use as a part of the keys for that map must override the hashCode() and equals() methods. (Well, you only have to override them if you're interested in retrievingstuff from your Map. Seriously, it's legal to use a class that doesn't override equals()and hashCode() as a key in a Map; your code will compile and run, you just won't find your stuff.)"

In the code below : The Cat class doesn't override hashCode() and equals() but still able to retrieve(find) the stuff. It's it a contraction to k&B statement?

package temp;
import java.util.*;
 
class Cat
{
 String name;
 Cat(){}
 Cat(String n)
 {
 name =n;
 }
}
 

class Temp
{
 public static void main(String args[])
 {
    Map<Cat,String> m = new HashMap<Cat,String>();
    String s1 = "A";
    Cat c1 = new Cat("B");
    m.put(c1,s1);
    
    System.out.println(m.get(c1));
 
 }
}

[wise owen]

    
  public static void main(String args[]) {    
    Map<Cat,String> m = new HashMap<Cat,String>();
    String s1 = "A";
    Cat c1 = new Cat("B");   
    m.put(c1,s1);
    [B]Cat c2 = new Cat("B");[/B]
    System.out.println(m.get(c2));
  }

[Sandeep Vaid]

Can you explain the output of your code.
I think here Object class's hashCode() comes into picture.

Please specify which is your key. The c1 object or it's name variable.

If c1 object is the key, then it's fine as unique key. and as c2 is difference key you got null.

[Naveen Zed]

Here, We want to get the meaningfully equal Cats(c1,c2 are equal in our sense) String that is "A".But this not catching the Cat That have a name as "B",but referring another Cat.So, the Item to the corresponing to the given key is not there(According to JVM),then surely the answar will be null.
Best example given by-- wise owen,Thank you.