I think String pool in Method Area, not in Heap. Need for Immutable String in Java. Once you create a String object and later decide to change the password, there is no way you can empty out the string.You can only make the string eligible for garbage collection. Java String objects are immutable. This question has been asked in a number of interviews in the past and is still being asked. In String class, it has the following code: private int hash;//this is used to cache hash code. Suppose we have multiple reference variables, all are pointing to the same object, if String is not immutable and we change the value of any reference then all others reference will get affected. I’ll be explaining about immutable classes, their advantages, how to create them, and finally why string class is immutable. causeProblem(s); Immutable objects are naturally thread-safe. The string is made final to not allow others to extend it and destroy its immutability. Basically Immutable itself means unmodifiable or unchangeable. String string1 = "abcd"; If String is not immutable, changing the String with one reference will lead to wrong value for the other references. string is widely used as parameter for many java classes, e.g. The string is Immutable in Java: In this post, we are going to understand another important concept. Read more posts by this author. The method thought it was connecting to one machine, but was not. String is an immutable class in Java. String string2 = "abcd"; If a string is mutable, changing the string with one reference will lead to the wrong value for the other references. Different threads can access a single "String instance". In every java interview definitely you will face Why String is Immutable in Java, Or can you list down few secret of String? And don't forget - not only are Strings immutable. String in Java (Why String is Immutable in Java) String, which are widely used in any programming language as Java. coz if one object makes any changes in reference value, its going to create a new reference only then other thread who is race condition will be referring to the previous reference address and previous reference value. One interesting topic to pursue is that javac itself is written in java, and why that may have impacted the decision to make Strings immutable in Java. You can also refer http://java-journal.blogspot.in/2010/12/why-strings-in-java-are-immutable.html. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference. Here are some of the points to explain the reason behind the design decision to make String immutable in Java. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object. Requirement of String Pool. 2) Performance: I believe that it is not the immutability of String class that gives it performance, rather it is string pool which works silently behind the scene. Developed by JavaTpoint. There are many advantages of immutable classes. Re: Why is String and Wrapper Classes are immutable in Java????? 807595 Nov 17, 2003 1:49 PM ( in response to 807595 ) Joshua Bloch's excellent book Effective Java … Let's understand the concept of string immutability with an example. In Java immutable objects are those whose data can’t be changed or modified (once modified). For example, if one client performs an action and changes the string value from Pressure to PRESSURE, all remaining clients will also read that value. Java runtime maintains a String pool that makes it a special class. String pool (String intern pool) is a special storage area in Method Area. 10, Aug 18. If any changes performed by anyone reference then other references will be impacted. Class java.lang.String is also final. There are many advantages of immutable classes. Why String is immutable in java String class is immutable in java. That’s why String objects are immutable. Why string is immutable in java? This means that once a string is created, it is not possible to modify it. Here the question is why String is immutable in java? That’s why String objects are immutable. What exactly is the meaning? String is a sequence of characters. Why is String immutable in Java. In Java, String is a final and immutable class, which makes it the most special. Great summary about why string is actually immutable type… Thanks, class Check{public static void main(String j[]){String s1=”JOHN”;//line no5String s2=”JOHN”;//line no6//s1.concat(“JOHN”);// line no 7//s1=s1+s2; /line no 8System.out.println(“Value of S1=”+s1);}}, in line no 7 if i compile it then it will print only JOHN but in line no 8 if i compile then it print JOHNJOHN why ?can anyone explain please, here foo and bar are pointing to the same memory location contains value “foo” when bar is initialised as “bar” separate memory is located to hold value “bar” . Java String class is immutable which means once a String object is created it cannot be changed. Why String is Immutable and Final in Java, Why String is Effective Immutable not Completely Immutable, How to break String's Immutability, Disadvantages of String Immutability, Why to use char[] array instead of String to store passwords For example, in a HashMap or HashSet. 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