Why String is immutable in java String class is immutable in java. String pool (String intern pool) is a special storage area in Method Area. Here the question is why String is immutable in java? This way Java Runtime saves a lot of heap space because different String variables can refer to the same String variable in the pool. If you search google for this question you will find people trying to answer this question. The String is immutable in Java because of the security, synchronization and concurrency, caching, and class loading. For example, if one client changes the value of the String "Test" to "TEST", all other clients will also see that value as explained in the first example. If we want that it refers to the HelloWorld, we have to explicitly assign it to that variable. 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 An obvious question that is quite prevalent in interviews is “Why Strings are designed as immutable in Java?”James Gosling, the creator of Java, was once asked in an interview when should one use immutables, to which he answers:He further supports his argument stating features that immutability provides, such as caching, security, easy reuse without replication, etc.In this tutorial, we'll further explore … 5 Reasons of Why String is final or Immutable in Java Though true reasons of why String class was made final is best known to Java designers, and apart from that hint on security by James Gosling, I think following reasons also suggest Why String is Final or Immutable in Java. This is more efficient. } All information in an instance is initialized when the instance is created and the information can not be modified. Let us refer to below example: “Test” can be referred by many reference variables. for(String a: set) Hey, this article is about mutability and immutability in Java. How can immutable object be a thread safe!? eval(ez_write_tag([[580,400],'programcreek_com-medrectangle-4','ezslot_2',137,'0','0'])); The following code will create only one string object in the heap. It means Strings were immutable that’s why java is still around in the game. But at the same time, string pool is not a possibility without making String class immutable. By the way, I have also shared my thoughts about String class in Java, you may find it useful. 5 Reasons of Why String is final or Immutable in Java Though true reasons of why String class was made final is best known to Java designers, and apart from that hint on security by James Gosling, I think following reasons also suggest Why String is Final or Immutable in Java. String has been widely used as parameter for many Java classes, e.g. In the case of String, several references can point to the same object. The. String objects in Java are immutable that means you cannot change the content of a string once they created. throw new SecurityException(); I think it may be some useful: http://newtechnobuzzz.blogspot.in/2014/07/why-string-is-immutable-or-final-in-java.html, I don’t agree with the following statement “This is also the reason why immutable classes are preferred in general”. In Java immutable objects are those whose data can’t be changed or modified (once modified). If several references point to same String without even knowing it, it would be bad if one of the references modified that String value. The term Mutable means "can change" and Immutable means "cannot change". String class is immutable i.e. All rights reserved. To really answer this question we will have to ask the designers of the Java language because only they can answer this questions. Let's discuss how these things work. At that time change in the string may result in loading … a.value = "a"; In this example, if String is mutable, its value can be changed which would violate the design of set (set contains unduplicated elements). 1. This was a design decision and I think a good one as Strings constitute about 20-40% of an application footprint. Why String pool in Java Heap? i.e. The primary basis of languages like c++, java, python etc is mutability. Some people, being skeptical, will put their hands in the fire, get burned, and learn not to put their hands in the fire. In general, strings are used to represent the vital details like database connection URLs, username passwords etc. Why String is immutable? These are some more reasons of making String immutable: Let's understand the concept of immutable through an example. In summary, String is designed to be immutable for efficiency and security reasons. You can also refer http://java-journal.blogspot.in/2010/12/why-strings-in-java-are-immutable.html. In String class, it has the following code: private int hash;//this is used to cache hash code. Java.util.BitSet class methods in Java with Examples | Set 2. Immutable simply means unmodifiable or unchangeable. The String is immutable in Java because of the security, synchronization and concurrency, caching, and class loading. It is not possible at all in the case to have one string object/literal. Why is String immutable in Java. Java Object Oriented Programming Programming. String is immutable in java becuase we can’t modifiy or change it once it is created. Why String is immutable in java String class is immutable in java. Hey, this article is about mutability and immutability in Java. But no one has been able to answer it properly and no one except the Java designers can really answer. There are a number of factors that considered when the string was introduced in java. Requirement of String Pool. Basically Immutable itself means unmodifiable or unchangeable. 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. as well (e.g. This tutorial also discusss the best practises of using string concatenation with Java. String in the mostly used object in Java and in the heap there is a pool of string objects(String Memory Pool). January 30, 2017 January 20, 2018 T Tak Java, Java interview questions. The reason of making string final is to destroy the immutability and to not allow others to extend it. 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. In Java Once we created string object we cannot change and modify its data or state. That is why string is immutable in java? It causes a more important memory print, but in thé other hand you benefit from the advantages written here (i do not totally agree with security remarks, though). But at the same time, string pool is not a possibility without making String class immutable. “a”.equals(a.value) is the error-proof way to compare two strings. 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. String is an immutable class in Java. For the performance reason, caching of String objects was important, so to remove that risk, we have to make the String Immutable. Immutable types rule out a plethora of hard to find mistakes one can make where one involuntarily changed an objects member value by modifying the value obtained through a getter . for opening network connection, you can pass host and port as String, for reading files in Java you can pass path of files and directory as String and for opening database connection, you can pass database URL as String. Program to convert set of String to set of Integer in Java . string is widely used as parameter for many java classes, e.g. String is immutable in Java. ==== 3.1. The hashcode of a string is frequently used in Java. as the 1st point you have write string pool. An immutable class is simply a class whose instances cannot be modified. We can’t modify the state of an immutable object and if we try to modify it then it creates a new object. If you take dictionary meaning of immutable, it means unable to be changed or unchanging over time, so String is unchangeable or unmodifiable in java. For example, in a HashMap or HashSet. An immutable class is simply a class whose instances cannot be modified. 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. - DEV, object will always represent the same value, it can't be modified. If String is not immutable, changing the String with one reference will lead to wrong value for the other references. so now bar variable points to the new object contains “bar” value. Because java uses the concept of string literal.Suppose there are 5 reference variables, all refers to one object "Sachin".If one reference variable changes the value of the object, it will be affected to all the reference variables. For example Suppose there are 5 reference variables,all referes to one object “abc”.If one reference variable changes the value of the object, it will be affected to all the reference variables. Les avantages clés de garder cette classe immuable sont la mise en cache, la sécurité, la synchronisation et les performances. Why String is immutable in Java is one of the most frequently asked String Interview questions in Java, which starts with discussion of, What is String, How String in Java is different than String in C and C++, and then shifted towards what is immutable object in Java , what are the benefits of immutable object, why do you use them and which scenarios should you use them. 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. These are two different things in memory. 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