Doubt in collection

[Lata Bagga]

 
 import java.util.*;
class Dog {
public Dog(String n) { name = n; }
public String name;
public boolean equals(Object o) {
if((o instanceof Dog) &&
(((Dog)o).name == name)) {
return true;
} else {
return false;
}
}
public int hashCode() {return 4; }
}
class Cat { }
enum Pets {DOG, CAT, HORSE }      
 
public class MapTest  {
 
public static void main(String[] args) {
Map<Object, Object> m = new HashMap<Object, Object>();
m.put("k1", new Dog("aiko")); // add some key/value pairs
m.put("k2", Pets.DOG);
m.put(Pets.CAT, "CAT key");
Dog d1 = new Dog("clover"); // let's keep this reference
m.put(d1, "Dog key");
m.put(new Cat(), "Cat key");
System.out.println(m.get("k1")); // #1
String k2 = "k2";
System.out.println(m.get(k2)); // #2
Pets p = Pets.CAT;
System.out.println(m.get(p)); // #3
System.out.println(m.get(d1)); // #4
System.out.println(m.get(new Cat())); // #5
System.out.println(m.size()); // #6

}
}

which produces something like this:
Dog@1c
DOG
CAT key
Dog key
null
5

If we add two lines of code to the end of the earlier MapTest.main(),

d1.name = "magnolia"
System.out.println(m.get(d1));

we get something like this:
Dog@4
DOG
CAT key
Dog key
null
5
null

I am really confused why the output is "null" after setting d1.name="magnolia", I suppose the output should be "Dog key". I have compiled this code but still confused how it is working.

[Vishwanath Krishnamurthi]

Hi,

Yes, it should print Dog Key and it does... I tried..
Guess you just forgot to save the changes before compiling again

Regards,
Vishwa

[sridhar row]

murthy are you sure??

[Vishwanath Krishnamurthi]

Hi Sridhar,

After adding those lines,

 import java.util.*;
class Dog {
public Dog(String n) { name = n; }
public String name;
public boolean equals(Object o) {
if((o instanceof Dog) &&
(((Dog)o).name == name)) {
return true;
} else {
return false;
}
}
public int hashCode() {return 4; }
}
class Cat { }
enum Pets {DOG, CAT, HORSE }      
 
public class MapTest  {
 
public static void main(String[] args) {
Map<Object, Object> m = new HashMap<Object, Object>();
m.put("k1", new Dog("aiko")); // add some key/value pairs
m.put("k2", Pets.DOG);
m.put(Pets.CAT, "CAT key");
Dog d1 = new Dog("clover"); // let's keep this reference
m.put(d1, "Dog key");
m.put(new Cat(), "Cat key");
System.out.println(m.get("k1")); // #1
String k2 = "k2";
System.out.println(m.get(k2)); // #2
Pets p = Pets.CAT;
System.out.println(m.get(p)); // #3
System.out.println(m.get(d1)); // #4
System.out.println(m.get(new Cat())); // #5
System.out.println(m.size()); // #6
                                    d1.name = "magnolia";
                                     System.out.println(m.get(d1));

}
}   

I'm pasting the o/p:

Dog@4
DOG
CAT key
Dog key
null
5
Dog key

[sridhar row]

Thanks Murthi, my bad ..my hashcode was returning name.length() which would be different for different names hence i was getting null..sorry abt the confusion.