doubt with string abjects

[Moieen Khatri]

Hi,

Can some one explain the below code where the number of string objects created is 3.I feel the objects created should be more than 3.Please clear my doubt.

Thanks

 public String makinStrings() {
 String s = �Fred�;
 s = s + �47�;
 s = s.substring(2, 5);
 s = s.toUpperCase();
 return s.toString();
 }

[ February 25, 2008: Message edited by: Moieen Khatri ]

[Kaydell Leavitt]

At first, I couldn't compile the code until I changed the double-quotes from curly-quotes to standard ASCII straight-double-quotes.

Now, it compiles and I get an output of:

ED4

[Nadeem Khan]

 public String makinStrings() {
 String s = �Fred�;
 s = s + �47�;
 s = s.substring(2, 5);
 s = s.toUpperCase();
 return s.toString();

Keeping in mind that String objects are immutable, total String objects created here - 5 ( fred, 47, fred47,ed4,ED4)

[Ian Edwards]

There are 6 String objects created here. You have to remember that s.toString() also creates a String object.

[rajaraman navaneethan]

Hey Moieen Khatri,
The number of objects created here is 5.To find the number of unique objects created you can use the following in your code.

class test
{

public static void main(String args[])
{

System.out.println(makinStrings());
}

public static String makinStrings() {
String s = "Fred";
System.out.println(s+" "+s.hashCode());
s = s + "47";
System.out.println(s+" "+s.hashCode());
s = s.substring(2, 5);
System.out.println(s+" "+s.hashCode());
s = s.toUpperCase();
System.out.println(s+" "+s.hashCode());
s=s.toString();
System.out.println(s+" "+s.hashCode());
return s;
}

}

I have just a call to the hashCode() method every time I make a change to the String Object s.When I run the above code , I get the following output.

bash-3.00# java test
Fred 2198155
Fred47 2112428622
ed4 100213
ED4 68469
ED4 68469
ED4

This shows there are 5 unique String Objects created since the hashCode() method returns different values each time it is called.

Hope this Helps.

regards,
Raja

[vaibhav srivastava]

I think you are missing the string "47" and thats why your count is less by 1 !!!

[rajaraman navaneethan]

Yes Vaibhav,
I missed out that 47.Thanks for pointing it out.

Raja

[Moieen Khatri]

thanks all for making the solution so simple by using the hashcode method

[rajaraman navaneethan]

Hey Ian,
I the toString() method does not seem to create a new String object.The hashCode() method returns the same value for toUpperCase() and toString() method.
So the total number of Objects created should be five.

regards,
Raja

[kamal shah]

Yes Raja,Agree with you ....total number of object created should be 5.toString() is returning the same reference of that object rather than creating new object.

[Deepak Chopra]

Well There are two ways to look into this question:

1) How many objects are created when this method is compiled and invoked ?

Answer : 5 (Already explained)

2) How many Object are created when this method is invoked..that means run time?

"Fred" and "47" Objects are created at compile time, So only 3 Objects will be created at run time and 2 Objects are created at compile time( in String Constant pool).