What is Java String Pool?

Filed Under: Java

As the name suggests, String Pool in java is a pool of Strings stored in Java Heap Memory. We know that String is special class in java and we can create String object using new operator as well as providing values in double quotes.

String Pool in Java

Here is a diagram which clearly explains how String Pool is maintained in java heap space and what happens when we use different ways to create Strings.

String Pool in Java, string pool, java string pool

String Pool is possible only because String is immutable in Java and its implementation of String interning concept. String pool is also example of Flyweight design pattern.

String pool helps in saving a lot of space for Java Runtime although it takes more time to create the String.

When we use double quotes to create a String, it first looks for String with the same value in the String pool, if found it just returns the reference else it creates a new String in the pool and then returns the reference.

However using new operator, we force String class to create a new String object in heap space. We can use intern() method to put it into the pool or refer to another String object from the string pool having the same value.

Here is the java program for the String Pool image:


package com.journaldev.util;

public class StringPool {

    /**
     * Java String Pool example
     * @param args
     */
    public static void main(String[] args) {
        String s1 = "Cat";
        String s2 = "Cat";
        String s3 = new String("Cat");
        
        System.out.println("s1 == s2 :"+(s1==s2));
        System.out.println("s1 == s3 :"+(s1==s3));
    }

}

Output of the above program is:


s1 == s2 :true
s1 == s3 :false
Recommended Read: Java String Class

How many Strings are getting Created in the String Pool?

Sometimes in java interview, you will be asked a question around String pool. For example, how many strings are getting created in the below statement;


String str = new String("Cat");

In the above statement, either 1 or 2 string will be created. If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool. If there is no string literal “Cat” in the pool, then it will be first created in the pool and then in the heap space, so a total of 2 string objects will be created.

Read: Java String Interview Questions

Comments

  1. ahana says:

    why string object will also be stored in string pool wen it is created using new keyword..

    1. barada prasad says:

      String is immutable, which says contents can not be modified. Every immutable object are treated under the concept like pool.

      Since ” ” mark is identified(in new keyword use of creating string), so it will first check in pool if it is already present. If already present then it will no more create a new object with same content in pool.

      again as every new keyword creates object in heap, so again a string object will be created with content inside “” “”.

  2. Neshi says:

    Hi… i think there is a small mistake in :”If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool” – if you have already literal “Cat” in the String pool then only one element will be creared in heap memory…

    1. Sandeep Raja says:

      If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the heap

      1. virendra says:

        I think Sandeep and Neha both are right .

        “string literal “Cat” in the pool, then only one string “str” will be created in the heap”

        1. Rana says:

          Which is correct ? Already Cat is there in the pool. how many objects created? either 1 or 2 ? My assumption is 1 .

  3. Rhicha says:

    Hey,
    Nice read.
    I have a question though.
    So, if I create a string object with new operator, 2 objects are created one in string pool (if already not present in string pool) and other in heap, right? So that implies while creating string object with new, string pool is checked if the literal is already present.
    But doesn’t intern() does the same thing? i.e check in string pool if literal already exist, if not, create new literal

  4. Asish Bajpai says:

    @Shidram Jyoti

    its correct answer, I think. String class intern method also supports this.
    As per intern() method, it will check first in string pool if string exists or not that means “new String(“abc”)”
    will not create string in string pool otherwise why “new String(“abc”).intern();” require to check string in string pool if it would have been created string when new String(“abc”).

  5. Dhananjay says:

    e.g. “Test” has referenced by many reference variables, so if any one of them change the value others will be automatically gets affected i.e. lets say

    String A = “Test”
    String B = “Test”

    Now String B called, “Test”.toUpperCase() which change the same object into “TEST”, so A will also be “TEST” which is not desirable

    I found this on one website…please clear my doubt about this point.

    * I done the code but I get the original value of the A “Test” not a “TEST”. after doing uppercase

    1. Pankaj says:

      String is immutable. When you call toUpperCase(), a new string is created and assigned. The original string remains unchanged.

      If String would not have been immutable, String pool would not have been possible.

    2. Dhrity says:

      Even the original value of string B will also not change, the logic being immutability as said by @pankaj

    3. Paul says:

      After these two statements
      String A = “Test”
      String B = “Test”
      “Test” will be created in the memory.

      When you will apply A.toUpperCase(), because String is immutable, another String with value “TEST” will be created in the memory, but A will NOT point to it.
      It will point only if you will write something like this:
      A = A.toUpperCase().

  6. Mahdi says:

    I appreciate it
    perfect ever !!!

  7. Ramesh G says:

    String str = new String(“Cat”);

    It will create one String in Heap this is clear. Why it should check in String pool and if it is not there need to create one more.In this case 2 strings memory is allocated internally in the heap[String pool is also part of Heap].

    Please clarify this it is confusing me.Below one atleast explain more.
    In above statement, either 1 or 2 string will be created. If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool. If there is no string literal “Cat” in the pool, then it will be first created in the pool and then in the heap space, so total 2 string objects will be created.

    1. Dnyaneshwar Chavan says:

      Author has written wrong sentence in his post. Wrong sentence is
      “If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool. ”

      the sentence should be
      “If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the heap.”

      Detailed explanation is –

      String pool is also part of heap.
      So the string will always be created in heap. But string may be or may not be created in pool.

      String str = new String(“Cat”);

      So in above sentence, if “Cat” is present in string pool, it will only be created in heap and will not be created in String pool.

      But if it is not present in String pool it will be created in string pool as well as heap space (or we can say space apart from String pool)

  8. Hayk says:

    “In above statement, either 1 or 2 string will be created. If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool.”

    Don’t you notice anything strange here?
    I think if there already exist one in the pool, then only one will be created only in the heep. will not it be?

    1. xj says:

      I noticed the strange part you pointed out. I feel that he made a mistake there

    2. TurboLoong says:

      I think so.

  9. PatrickInBama says:

    I thought the String Pool just consisted of the actual string value and then the reference to it, str, would be added tot he heap? The object using the string value should be contained in the Heap with the reference to the object on the stack. So the following:

    String str = new String(“cat”);

    Should only create one value in the string pool, not 2. “str” is the object containing the reference to “cat” on the pool and that object is in the heap with the reference to the object contained on the stack. If you said how many objects are on the heap, 2 would make sense, but to say 2 strings are created is misleading. The correct answer should be 2 objects, one on the pool and one on the heap is clearer.

  10. Vettaiyan says:

    In above statement, either 1 or 2 string will be created. If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool.

    will be created in pool or heap memory(outside pool)?

  11. Tukaram says:

    Hello Pankaj,
    Could you plea address below doubt?

    Lets say in my Java app I have one calss – A having method for String as setContent and getContent.
    Now Once I set the String Content using setter method, later I use that object of class A to get that String and put in List using getter method. where that list element will point ? to String pool or somewhere else?

    1. Pankaj says:

      If you will use String literal, it will point to String Pool. If you use new operator, then heap.

  12. salman says:

    String s1 = “Hello”.concat(“World”);
    String s3 = new String(“HelloWorld”); //Line-2
    String s2 = s1.intern();
    System.out.println(s1 == s2); //false
    System.out.println(s1 == s3); //false
    System.out.println(s2 == s3); //false

    If I removed Line-2 and compare s1==s2, it will return true. Could anyone explain me what exactly happens in string pool after Line-2?

    Thanks

    1. ZT says:

      if you use jdk1.7 or later, it will output “true”, and if you use jdk1.6, it will output “false”. Because String’s member function intern() ‘s behavior is different. In jdk1.7, it will check if there is a same literal in string constant pool. if yes, it will return the reference of this literal object. otherwise it will store the reference of string object created by new operator into the string constant pool and then return this reference. In your code snippet, String s3 = new String(“HelloWorld”) this sentence will create string “Helloworld” in string constant pool, then String s2 = s1.intern(); s2 will refer to this string object, so System.out.println(s1 == s2); it will output “false”. when you remove the sentence in line2, there is not literal “Helloworld” in string constant pool, so String s2 = s1.intern(); it will return the reference of object in heap, so output is “true”

      1. Saheb Jana says:

        “String s2 = s1.intern(); s2 will refer to this string object” why s2 will refer to the s3 instead of s1?

      2. Ankit says:

        Can you please explain, ‘How it checks that same literal is already there in the Pool?’, I mean what kind of data structure does it use for checking it, as there might me be many strings.

    2. Rahul Bawa says:

      String s1 = “Hello”.concat(“World”);

      This will create helloworld in pool as well as heap. Right ?

  13. Purushottam says:

    String s1= “old value of s1″;
    s1=”new value of s1”;

    Sysout(s1);

    It will give new value.
    Is it possible to get old value as same reference to two different literals are there.

    1. Vinay Kumar says:

      Not possible because as you write s1=”new value of s1″, s1 will now start pointing to “new value of s1” and we now don’t have any reference to “old value of s1”. So “old value to s1” will be lost.

  14. Shidram Jyoti says:

    String s1=new String(“abc”);

    Above line will create only one object in the heap, it won’t create two objects as you mentioned (one in heap and one in pool). To put the object in pool you need to call ‘intern()’ on this object, then it checks the pool for existence of this object in the pool, if not available then it will create one in the pool .

    Example : String s1=new String(‘abc”).intern();
    This will check the SCP for “abc” object, if not present then it will create this object and ‘s1’ reference will change to the SCP object and heap object will be dereferenced.

    Suppose if we change your code like this :
    String s1=new String(“abc”);
    s1.intern();

    Then this will just create the “abc” object in SCP, but this object will not referred by the reference variable ‘s1’ (as it’s not assigned to ‘s1’).

    I hope it’s more clear now.

    Kindly comment if someone having different understanding on the same so that it will help to get correct information on the same.

    Kindly update the article w.r.t above details, otherwise it will give wrong impression to the reader.

    1. Sam says:

      String s1=new String(“abc”);

      This above statement does create two objects. one in heap and another in String Constant pool. But the reference points to the heap object not to the one in the pool.

      1. Gajendra says:

        String s1=new String(“abc”).intern();

        What happen for above line?

        1. Mahesh says:

          It will create object in heap as well as in SCP

    2. Amit says:

      Hi Shidram Jyoti,
      Is there any way to validate your point that only one object will be created?
      Because all of the articles over the net says that two different objects will be created. One in Heap and other in String Constant Pool.

    3. Ravi Awasthi says:

      I think you explanation is correct. If We create String object using new it will create only one object. intern() method is use for create same heap object into constant pool.

  15. Very good example, Thanks for sharing.

  16. Gerrix says:

    On interview I was asked to explain string pool. Unfortunately I did not know answer. Its reason why I read this post. Tnx!

  17. Mithun C T says:

    Hi Pankaj,

    String abc = “a” + “b” + “c”;

    Here how many objects created in string pool memory?

      1. Rumi says:

        it’s four
        a, b, c, abc

        1. quyetnguyen says:

          I think only 3 : a, b and c. abc is stored in stack

          1. Dushyant Sheoran says:

            Hi quyetnguyen,
            Your explanation would be true if we were using String buffer or StringBuilder. But here there will be four if none already exists in the String pool.

          2. Abhishek Mishra says:

            Only One Object will be create

    1. Ryszard S says:

      One or zero. Java compiler will merge these three “a” “b” “c” strings into one “abc”. Then if string pool contains “abc” then none string will be created. Otherwise one string “abc” will be created.

    2. KK says:

      It will create only one string in the SCP.
      It merges a,b,c and creates abc.If it is not already there in the pool

      1. Damodara says:

        Who is correct?
        zero or one
        OR
        3 or 4??

        1. Damodara says:

          please refer the below:
          It creates only 1. The compiler does some work and merges to one before runtime.
          https://www.quora.com/How-many-objects-will-be-created-in-this-case-string-str-a+b+c-in-Java

  18. Mayur says:

    Hello,

    i have statement like as below please suggest hoe it will store in which memory,

    String s1 = “ABC”;
    String s2 = “ABC”;
    String s3 = s1;

    String s3 = new String(“ABC”);

    String s4 = s3;

    1. Shankara Nethran S N says:

      Hi,
      You will get an Compile Time Exception
      declaring like this

      String s3 = s1;

      String s3 = new String(“ABC”);

  19. nbsaw says:

    hi pankaj,

    I Could not understand the following sentencecan’t undestand it .

    If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool.

    why pool not heap?

    plz reply me thank you XD

  20. shravan says:

    hi pankaj,

    does StringBuffer also places object in string pool?

    StringBuffer sb=new StringBuffer(“abc”)

    how many objects are created with above line

    1. guest says:

      yes, it does. and it creates two objects.

  21. Mohamad says:

    When I create a String object with New operator and then use Intern() method, If String value not in Pool then add if exist in Pool then returned back reference.

    But what happens to the first memory created with New String(“test”)?
    (In Heap and outsize of Pool)

  22. Amol Aggarwal says:

    Is string pool part of heap. I thought it was part of method area which is actually different from heap. The first diagram shows it as a part of heap above.

  23. Deepak Kumar Sahu says:

    nice tutorials

  24. Jun Zhuang says:

    I have trouble understanding your following statement:

    String str = new String(“Cat”);
    In above statement, either 1 or 2 string will be created. If there is already a string literal “Cat” in the pool, then only one string “str” will be created in the pool. If there is no string literal “Cat” in the pool, then it will be first created in the pool and then in the heap space, so total 2 string objects will be created.

    If you do not intern str how could a string literal be created in the string pool? If you do and the “Cat” literal does not already exists in the pool, it will only be created in the pool not on the heap. If you have something like this:

    String str = new String(“Cat”).intern();

    then 0 or 1 string will be created depending on whether a “Cat” literal exists.

    Thanks,
    Jun

  25. Mayank Bhandari says:

    My idea is that if an object is in heap like this
    String s1=new String(“hello”);
    and let us say s1 holds address 123
    then i do this,
    s1.intern();
    still now s1 address 123 and holds the object “hello” in 123
    However one more String object “hello” (literal object) has been created whose reference is lets say 321. Now this reference is being stored in the constant pool table.
    Am I correct?

    1. Mayank Bhandari says:

      *String pool reference table, not constant pool table.

  26. Prashant Gawande says:

    question-Runtime constant pool and String pool are same thing or different ?

      1. pravin says:

        java doc says they are same

  27. Hiren Mistry says:

    class ClassM2{
    public static void main(String[] args){
    String s2 = “test”;
    String s3 = “test”;
    String s4 = s3+””;
    System.out.println(s2==s3);
    System.out.println(s3==s4);
    }
    }
    Why s3==s4 gives “false”? I know “test” string stores in String pool and s2 & s3 points to same reference. but why not s4? It also has value “test”. Please explain.

    1. Pankaj says:

      Because s4 is not created in Pool since Compiler puts string values in pool that are constant right from compile time. s4 value is dependent on s3 variable at runtime, hence it’s created in heap.

      Refer http://stackoverflow.com/questions/16729045/behavior-of-string-literals-is-confusing

      1. Prashant says:

        Awesome explation Pankaj… Thanks 🙂

  28. Manjunath says:

    Does String pool has divided into parts like constant pool and non-constant pool?

  29. shellbye says:

    great pictrue

  30. Adrian says:

    Another thing about the Java String Pool.

    For long term maintenance of your code you should use the “equals” method not the “==”. You may refactor the code and string pool object is replaced with a heap object and you get all kinds of problems. Refactor tools don’t “see” the cases where == should be changed to equal.

    primitive => ==
    objects => equals

  31. muni says:

    String s=”abc” ;—–creates a string object “abc” with reference ‘s’ in string pool.

    String s=new String(“abc”);—-creates a string object “abc” with reference ‘s’ in heap memory and also creates a string object “abc” in string pool without reference so here two objects are created then what is the necessity for creating String object using new operator?

    1. Anjani says:

      Good question. Anyone have explanation?

      1. Sabi says:

        public class Hash {
        public static void main(String[] args) {
        String s1=”cat”;
        String s2=”cat”;
        // Both String hashcode will be same if String content is same
        System.out.println(s1.hashCode());
        System.out.println(s2.hashCode());
        // After changing content of s1 String hashcode will changed
        s1=”dog”;
        System.out.println(s1.hashCode());
        System.out.println(s2.hashCode());

        }

        }

        1. shailendra tiwari says:

          here String literal created new object and pointing to s1 reference variable
          then new hashCode created………

    2. saroj says:

      it creates a reference in pool for feature used.

    3. Ajinkya Rane says:

      String s=new String(“abc”);—-creates a string object “abc” with reference ‘s’ only in heap memory and not in string pool.

  32. Teo says:

    Hi,

    I have one example which I found a little confusing. I understand that in context of String object type, by using NEW word, new object is created and when using “” in String initialization, String pool mechanizm is used.

    Why isn’t String pool used in following case?

    *******************
            String myStr = “good”;
           char[] myCharArr = {‘g’, ‘o’, ‘o’, ‘d’ };
            String newStr = “”;
            for(char ch : myCharArr){
                newStr = newStr + ch;         
    }
            boolean b1 = newStr == myStr;        
     boolean b2 = newStr.equals(myStr);                  

    System.out.println(b1+ ” ” + b2); (false true is printed)
    *******************

    Thx in advance,
    Teodor

    1. varun says:

      Dear Ravi,

      This is where “==” and .equals differ. “==” checks equality for hash code of objects reference while .equals compares their contents.

      Pls let me know if u have any confusion.

      1. Anupam says:

        String s1=”Hello”;
        String s2=”Java”;
        String s3=”Hello Java”;
        String s4=s1+” “+s2;
        String s5=new(“Hello Java”);

        System.out.println(s3==s4);// false! understood.
        System.out.println(s3.hashCode()==s4.hashCode()); true how?
        System.out.println(s3.hashCode()==s5.hashCode()); true how?

    2. Adrian says:

      You used the String equal() with a char[] array. char[] arrays are Object not String.

      This “newStr.equals(myStr)” compares a String with an array. When comparing 2 objects for “Equal” they should be of the same class. The equal method takes an Object but the methods usually make an instanceof check, cast to a specific type then compare the “this” with the “argument”.

      The rule of tumb for equal on the Java objects is: instanceof, cast then compare object internals. Of course you can implement any freaky equal but in general you should stick to the “contract”

      if you would have done:

      newStr.equals(new String(myStr))

      it would have worked because it makes a new String object out of the array and the object passed to the method is a String in this case.

    3. Deepak says:

      Hi Teo,

      If concatenate variable, so here hashcode always will be different.
      newStr, ch is variable.
      You must need to concatenate direct literal only, instead of variable means…….

      newStr = ‘g’+”ood”; result would be ‘true’.
      ‘g’ and “ood” is literal.

      I think it not possible in loop.

  33. Ravi says:

    Hi Pankaj,

    I am following you articles and finding it really precise. Really appreciate your efforts.
    But coming to this article, I have one doubts.

    The value in the String pool are “String” or reference to the String Object created in the Heap i.e. collection of references to String objects ?

    1. Pankaj says:

      String Pool contains String objects, remember that ‘reference’ variables always part of Stack memory, so obviously it can’t be in string pool that is part of heap memory.

      1. Ravi says:

        Hi Pankaj,

        I am understanding your point and agree to that.
        But after going throw a question on Stackoverflow , I am confused …
        “Is String Literal Pool a collection of references to the String Object, Or a collection of Objects”

        http://stackoverflow.com/questions/11700320/is-string-literal-pool-a-collection-of-references-to-the-string-object-or-a-col

        that is taken from
        http://www.javaranch.com/journal/200409/Journal200409.jsp#a1

        If possible, kindly have a look once and confirm from your end.

        Thank you.

      2. satish says:

        Hi pankaj,
        Can you please clarify me, how many objects will be created in below case and why?am slightly confused in this.

        String s1=”cat”;

        String s2=”cat”;

        String s3=”c”+ “at”;

        String s4= new String(“cat”);

        String s5=”kitty” + “cat”;

        String s6= new String(“kittycat”);

        String s7=s5;

        Thanks In Advance. 🙂

        1. Parvinder Singh says:

          Short Answer: 4 objects.

          Explanation below:

          String s1=”cat”; //1st object created in String Pool and s1 started referring to it

          String s2=”cat”; //s2 refers to the same String whom s1 refers to

          String s3=”c”+ “at”; //s3 refers to the same String whom s1 and s2 are referring

          String s4= new String(“cat”); //A new object (2nd) is created in Heap and s4 refers to it

          String s5=”kitty” + “cat”; //A new object (3rd) is created in string pool and s5 refers to it

          String s6= new String(“kittycat”); //A new object (4th) is created in heap and s6 refers to it

          String s7=s5; //s7 refers to same string whom s5 refers.

          1. Pradeep says:

            Suppose i do,
            String s1 = “cat”;

            String s8 = “c”;
            s8 = s8 + “at”;

            now,

            s1 == s8 getting false , not able to understand..

      3. Pete de Fina says:

        This is so interesting. My first program was creating rows that contained 3 types of datapointers.

        Row = new(Prow ) >> First Row instantiated; Pointer Row in the STACK refering to it .

        But then the second row:

        ThisRow = Row;
        ThisRow^.next = new(Prow) >> Now I am instantiating by pointer ‘next’ which is part of object (1st row) that exists in the HEAP, but was already defined in object.

        Instantiating 100 times, using ref. called ‘next’, you go deeper and deeper in the heap. Can you still say ref. variables are always stack variables?

      4. Anushree says:

        So, after the method execution is over, all local String references will be nullified and the objects in the heap will be garbage collected. is it?

    2. Dhananjay says:

      Nice explanation Pankaj..

  34. Satish says:

    Hi ,
    Can you please clarify me, how many objects will be created in below case and why?

    String s1=”cat”;

    String s2=”cat”;

    String s3=”c”+ “at”;

    String s4= new String(“cat”);

    String s5=”kitty” + “cat”;

    String s6= new String(kittycat);

    Thanks In Advance. 🙂

    1. Biswajit sahoo says:

      7 objects

      1.”cat”
      2.”c”
      3.”at”
      4.new String(“cat”);
      5.”kitty”
      6.”kittycat”
      7.new String(kittycat)

  35. Timofei says:

    Thanks. But reply form is too far from article. I can forget my answer during scrolling down )

    1. Pankaj says:

      Reply form after comments, so that people can read others comments first. Chances are you will find your queries answered in some of the comments, saves time.

    2. rojaja says:

      Timofei, ever heard of Ctrl+End ? It will take you directly to the end of the page

  36. Pranita W says:

    String s=”abc”;
    s = s+”def”;
    System.out.println(“String Result:- “+s);//output – String Result:- abcdef

    In this case content of ‘s’ variable is getting changed but according to java concept String is immutable.
    So,can you please explain me what happen with ‘s’ variable in the string pool?

    1. Sarika says:

      When you write String s=”abc” at this point s refers to string whose value is “abc”.

      When you write s=s+”def” a new string “abcdef” is created and s now refers to this new string and not to “abc”.
      Hence originally created “abc” string remains unchanged. It remains as it is in pool.Hence strings are called immutable.

  37. Pradeep Singh says:

    Pankaj,

    Is there any way to get the size of String Pool?

  38. Karuppasamy says:

    package com.journaldev.util;

    public class StringPool {

    /**
    * Java String Pool example
    * @param args
    */
    public static void main(String[] args) {
    String s1 = “Cat”;
    String s2 = “Cat”; // here s1 & s2 value Cat stored into String Constant pool only once, so no doubt.
    String s3 = new String(“Cat”);
    String s4 = new String(“Cat”) ; // my question is here. here s3 & s4 value Cat is two times created into normal pool or only once created into normal pool.
    System.out.println(“s1 == s2 :”+(s1==s2));
    System.out.println(“s1 == s3 :”+(s1==s3));
    System.out.println(“s3 == s4 :”+(s3==s4)); // here both value of hashCode same but why to be false?

    }

    }

    1. Pankaj says:

      s3 and s4 will be referencing to two different objects. == checks if reference is same, that’s why s3==s4 is false.

      1. xiaocai607 says:

        s3 == s4 will return true, have you try it? I have, it is true even I think it should not

        1. xiaocai607 says:

          Please ignore my comments

    2. Vishal Nikam says:

      If s1 & s3 “Cat” objects are created in Heap & SCP area respectively and (s1==s3) returning false that is correct but why their hascodes are same then? If hashcodes are same means both references are pointing to same object then (s1==s3) should have returned true ideally?

      Please clarify on this.

      public static void main(String[] args) {
      String s1 = new String(“Cat”);
      String s3 = “Cat”;
      System.out.println(s1.hashCode() + ” && ” + s3.hashCode());
      }

      O/P :

      67510 && 67510

      Regards,
      Vishal

      1. Pankaj says:

        hashcode has nothing to do with object reference.

      2. Biswa says:

        check with

        System.identityHashCode(s1);
        System.identityHashCode(s3);

        it will help u

  39. Amir hossein says:

    In the name of god.

    public static void main(String[] args)
    {
    String s1 = “Cat”;
    String s2 = “Cat”;
    String s3 = new String(“Cat”);
    String test;
    System.out.println(“s1 == s2 :”+(s1==s2));
    System.out.println(“s1 == s3 :”+(s1==s3));
    }

    hi, how to return value(No address) from heap(s3) to stack(test).
    Thanks.

  40. balinder says:

    Thnx for the post. helped to clarify a lot of things

  41. sanjaya verma says:

    public class MainDemo {

    public void comp() {
    String s1=”India”;
    String s2=”India”;
    String s3=new String(“India”);

    System.out.println(“== result:” + s1==s2); // false
    System.out.println(“equals result:” + s1.equals(s2)); // true
    System.out.println(“****************”);
    System.out.println(“== result:” + s1==s3); // false
    System.out.println(“equals result:” + s1.equals(s3)); // true
    }

    /**
    * @param args
    */
    public static void main(String[] args) {
    // TODO Auto-generated method stub
    MainDemo obj=new MainDemo();
    obj.comp();
    }
    }
    Question – what is the difference between s1==s2 and s1==s3 , => both returns same result.
    but in your post s1==s2 is true that is not right result. I have checked this by writing same program in to this post. So plz clear my doubt ??

    1. Pankaj says:

      “== result:” + s1==s2

      + operator priority is more, so it will result in "== result:India"=="India" and hence false. I hope it will clear your confusion.

      1. balinder says:

        to get the desired result you can write:
        System.out.println(“== result:” + (s1==s2) );

  42. krishna says:

    If for example:

    String str1 = “abc”;
    String str2 = new String(“def”);

    Then,
    Case 1: String str3 = str1.concat(str2) will go in the heap or pool?

    Case 2: String str4 = str2.concat(“HI”) will go in the heap or pool?

    1. krishna says:

      will be creating the new object in the string pool,

      1. Maaniccka Poonkundran says:

        If it is creating in the pool, then the following code should output “True”. But it is not?

        String str1 = “abc”;
        str1 = str1.concat(“d”);
        if(str1 == “abcd”)
        System.out.println(“True”);

        1. Alok Chandna says:

          try this
          String str1 = “abc”;
          str1 = str1.concat(“d”).intern();
          if(str1 == “abcd”)
          System.out.println(“true”);

          the object are not placed in pool automatically, unless intern is called.
          so when you call intern above “abcd” is placed in pool and when it program encounters the literal “abcd” it finds it in the pool and hence the references are equal

  43. Ashish says:

    String s = “ashish”;
    String b = new String(“ashish”);
    b.intern();
    System.out.println(s==b);

    if string pool is manged then why not string ‘s’ reference is returned on b.intern() to b. It is printing false which means their reference are not same.

    1. Pankaj says:

      You need to write b = b.intern();, see you haven’t updated the reference of “b” variable.

    2. vinod says:

      intern() method return a String .
      but in case of you does not hold return of intern ().

  44. Ganesh says:

    How come String Pool has two Cat literals and is Stringpool a part of Heap?

    1. Pankaj says:

      Corrected the image, yes String Pool is part of Java Heap memory.

      1. Ganesh Rashinker says:

        String str1 = “abc”;//reference is checked on constant pool
        String str2 = new String(“abc”);//reference is checked on heap
        System.out.println(str1 == str2);//returns false
        //that is why we use intern
        str2 = str2.intern();
        System.out.println(str1 == str2);//return true as both are pointing to string pool
        //String pool is a part of constant pool and memory is getting allocated in Method Area whereas when we use new operator memory is getting allocated in heap.
        //Note: Methos area can be a part of heap or a seperate memory area. this depends on JVM implementation.

        1. Ganesh Rashinker says:

          Please check this blog for a demo of what I have mentioned above. Please correct me if my understanding is wrong somewhere.

          http://ganeshrashinker.blogspot.in/

  45. kunal says:

    I have one confusion,

    when we create a new String Object like String s = new String (“abc”);

    As far as I know, this will create a new String Object in Heap and also abc will go in String constant pool

    and s will point value exists in string constant pool…
    which means the value already exists in String Constant Pool, so what will intern do in this case?

    Also String Constant Pool is not a part of Java Heap Memory..?

    1. Pankaj says:

      When we use new keyword to create the String object, it doesn’t go into the String Pool. When we call intern method, then it checks if any String with same value is already present in the pool or not. If there is already a String with same value, it returns the reference or else it places the String into the pool.

    2. Ganesh Rashinker says:

      Hi Kunal, you can refer below snippet
      String str1 = “abc”;
      String str2 = “ab”;
      String str3 = “c”;
      String str4 = str2 + str3;//using StringBuilder for concatenation and returns new String object
      System.out.println(str1 == str4); // returns false
      str4 = str4.intern();
      System.out.println(str1 == str4); // returns true

      1. Mahrshi says:

        Hi Ganesh,

        I have two questions :-

        1) Why the below line is returning false, It should return true because when str4 will create than first it will check in string pool whether any other string value is present or not with the same value. If str1 is already there with the same value than it should refer the same reference as str1 has.

        System.out.println(str1 == str4); // returns false

        2) In your above example “intern” method you are using for string pool as str4.intern().

        Can we use “intern” method for string pool also?

        1. johny says:

          I am also having the same doubt # 1. Somebody please reply who knows the correct answer?

          1. balinder says:

            string concatenation(using + operator) is same as creating new String object fr eg:-

            String s1=”abc”;
            String s2=”def”;
            String s3=s1+s2; // It is same as String s3 = new String(“abcdef”);

    3. vinod says:

      in frist question You are Right.
      when we create String by new keyword then one will go to heap and another in String pool

      String constant pool is depend on the JVM. architecture

  46. siddu says:

    Could you post some example on intern() method.

  47. Ridham Shah says:

    Where the string stored.Means location of string where it stored.

  48. abhay agarwal says:

    hi .. excellent post … one correction – “we force String class to create a new String object and then place it in the pool.” here, new operator creates object in Java heap, not in pool.

    1. Pankaj says:

      String Pool only contains reference to the String objects. The text means the same thing.

      1. Abhi says:

        Hi Pankaj,
        so do you mean that String pool only contains reference to string but not actual value/string ?

      2. rojaja says:

        You are contradicting yourself here. First you said String objects live in the pool, now you say only the references do. So where do the objects (values) they reference to live ? In your image you have the actual values inside the pool.

    2. Rishi Raj says:

      Yes, Pankaj. Please update this post accordingly. Your other posts also say so.

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