StringBuffer

[Dayanand]

package mutable;

public class Expt
{

public static void main(String[] args)
{

StringBuffer sb = new StringBuffer();
sb.append("abc");
sb.append("xyz");

StringBuffer sb1 = sb.append("123");
System.out.println("sb1->"+sb1);
System.out.println("sb->"+sb);
System.out.println(sb==sb1);
System.out.println(""+sb==""+sb1);

}

}

output
sb1->abcxyz123
sb->abcxyz123
true
false


what makes the difference between the below to statements
System.out.println(sb==sb1);
System.out.println(""+sb==""+sb1);

why (" "+sb==" "+sb1) is false

Thanks in advance
Daya

[masijade]

You are comparing references not values with == and in the second one new objects are being creted due to the string concatenation and these new objects have different reference values even though the actual string values are the same.

IOW do not use == to compare objects (of any kind) unless you wish to see if those variables reference the exact same object. If you wish to compare the values of the objects behind those references use the equals method.

[Dayanand]

thanks for your valuable solution

one more doubt
but i think no new objects will be created in case of StringBuffer,has StringBuffer provides Mutable objects
can u please help me out in this case.?

[masijade]

Doesn't matter. String concatenation (which is what that + causes in that form) produces Strings not StringBuffers.

Edit: And, it doesn't really matter what that + produces, nor does it matter that mutable objects were fed into it, it produces new objects.

[Dayanand]

sorry Sir,for asking u again and again.!!!!!!!!!!
System.out.println(""+sb==""+sb1);
""+sb will provide one string
""+sb1 will provide one string

but at last sb & sb1 strings will have same content, but why it results in false when sb==sb1 is checked

[masijade]

sorry Sir,for asking u again and again.!!!!!!!!!!
System.out.println(""+sb==""+sb1);
""+sb will provide one string
""+sb1 will provide one string

but at last sb & sb1 strings will have same content, but why it results in false when sb==sb1 is checked

Because they are different objects. I.E. they are represented by different structures on the heap even though those structures contain the same value they are still different structures and so have different "addresses" and == compares these "addresses" not the values of the structures behind those "addresses".

[Dayanand]

Because they are different objects. I.E. they are represented by different structures on the heap even though those structures contain the same value they are still different structures and so have different "addresses" and == compares these "addresses" not the values of the structures behind those "addresses".

System.out.println(""+sb.equals(""+sb1));
out-put
false

has equals() method will check content then why (""+sb.equals(""+sb1)) results in false

[Dayanand]

as already mentioned, when you compare two objects with == you are comparing its references and not the content.

System.out.println(""+sb.equals(""+sb1));
out-put
false

has equals() method will check content then why (""+sb.equals(""+sb1)) results in false

[masijade]

Because you are comparing sb to ("" + sb1) and prepending "" to that result, you are not comparing ("" + sb) to ("" + sb1)

(""+sb).equals(""+sb1)

[Dayanand]

Because you are comparing sb to ("" + sb1) and prepending "" to that result, you are not comparing ("" + sb) to ("" + sb1)

(""+sb).equals(""+sb1)

very very very superb
really i am very thankful for spending your valuable time for my doubts

Thanks a lot Sir
Daya