qureis on scja

[paarul saxena]

i hava a trouble with a few programming questions...would be grateful if someone helps out..
supposedly a program construct creates two new instances as given below:
class Dog{
String name;
public static void main(Sting []args){
Dog d1=new Dog();
Dog d2=new Dog();
d1.name="aiko";
d2.name="aiko";
if(d1.equalsd(2))
System.out.println("true");
}
}
why no output is produced when according to mackenzie book it gives true??

[Igor Lichs]

Is its output really "true" ?

As far as I know, the equals melhod defined in the Object class compares hashCodes.

I just made some implements in your code to print the hashCode:

class Dog{
String name;

public static void main(String []args){
Dog d1=new Dog();
Dog d2=new Dog();
d1.name="aiko";
d2.name="aiko";
if(d1.equals(d2))
System.out.println("true");

System.out.println("hC1: " + d1.hashCode() + "\nhC2: " + d2.hashCode());
}
}

and the output is:

hC1: 25669322
hC2: 14978587

so their hashCodes are different and this code will never output a "true" message.

are you sure this is all the code?

[chander shivdasani]

According to my knowlegdge, the equals method of the String class behaves differently when compared to others. If the same thing was implemented on String objects, the result would have been true.

for example.

String s1 = new String("Hi");
String s2 = new String("Hi");

if(s1.equals(s2))
{
SOP("True");

}

In the above case, the output will be true.

Correct me if i am wrong.

And the equals method of the object class compares the hash codes.

[Ankit Garg]

the equals method of Object class just checks

this == obj

and not

this.hashCode() == obj.hashCode()

You can try it by implementing the hashCode method that returns 1 and don't implement the equals method. then also it will return false(i.e. even though every object will have equal hash code)...

In your case since the answer will be false...there is no chance that the answer is true. I have tried the code...

Your code also has some errors...String has been written Sting in main() and d1.equals(d2) has been written d1.equalsd(2)