Strange behaviour in String equality comparison.

Question

Assume these variables:

String a = "hi";
String b = "hi";
String g = a + b;
String f = "hi" + "hi"
String h = "hihi";

these are the comparison results:
(a == b) : true
(g == h) : false
(f == h) : true

what is happening here? are string imediates different from string variables in comparison?

you can see the results here:
https://code.sololearn.com/c8crILfg4FTb/?ref=app

Answer 1

if you used
"=="
it compair the reference id of object in pool area

and pool area have some characteristics
1.->in pool area GC does not work.
2.duplicate object not allowed.

now see you problem

a="hi";
b="hi"
c=a+b
f="hi"+"hi"
h="hihi";

so
for frist command execution that happen.

1000-->address of memory
[hi]-->name of memory is a

1000
[hi]-->name of memory is a and b
note here new object is not created.

2000-->address of memory g
[a+b]-->name of memory is g

3000 -->address of memory f
[hihi]-->name of memory f

and variable h point the same location same as f
it mean that

f==h--> give you output true because they point same address like 3000.

a==b-->give the output true
because they point the same address like 1000

now
when you do this
String a=new String("hi");
how many object is created by this code
that ans is two
one in heap
2000
[1000]
heap object store the reference id of pool object

and second one in pool
1000
[hi]

Answer 2

Mayank Rampuriya you're welcome ✋😊

Answer 3

Arun Tomar thanks for your complete explanation. now I get it 👍

Answer 4

use . equals() not ==

Answer 5

this is because '==' checks if the reference to an object is the same.
a and b are pointing to the same place in memory.
g is a reference to a new place, created especially to store the result of a+b
f and h are equals due to optimisation by the compiler (possible because they are initialized with hard coded strings)
The method equals() can be used to compares the content.

Answer 6

This thread cleared my doubt too!
Thanks Amir

Answer 7

Are you using .equals instead of ==?