If any changes performed by anyone reference then other references will be impacted. If String is not immutable, changing the String with one reference will lead to wrong value for the other references. The immutability of strings helps to keep such details unchanged. Let’s see why String is immutable in java. Java String objects are immutable. An Immutable Object means that the state of the Object cannot change after its creation. What is String immutability? Description: We can understand the above example with the help of the following diagram: In the string constant pool, the Hello remains unchanged, and a new string object is created with HelloWorld. Let’s see why String is immutable in java. The String is the most widely used data structure. network connection, opening files, etc. 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. Eventually, immutable means that you are not able to change “bar” value (for example, if you want to add a letter to “bar”, you have no other choice than creating a new instance of a string : you can t reuse the “bar” instance. This way Java Runtime saves a lot of heap space because different String variables can refer to the same String variable in the pool. There are dozens if not hundreds of discussions on the web about why Java Strings are immutable. 14, Aug 16. Because immutable objects can not be changed, they can be shared among multiple threads freely. Java.util.BitSet class methods in Java with Examples | Set 2. 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). String in the mostly used object in Java and in the heap there is a pool of string objects(String Memory Pool). In Java immutable objects are those whose data can’t be changed or modified (once modified). Class java.lang.String is also final. as the 1st point you have write string pool. 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 If you search google for this question you will find people trying to answer this question. String is widely used as a parameter for many java classes, e.g. How can immutable object be a thread safe!? There are many advantages of immutable classes. String is immutable in java becuase we can’t modifiy or change it once it is created. That is the reason why bar variable has been assigned the “bar” value after having been assigned the “foo” value first. Why String is immutable in Java? All information in an instance is initialized when the instance is created and the information can not be modified. Immutable simply means unmodifiable or unchangeable. In java, string objects are immutable because String objects are cached in String pool. 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. But at the same time, string pool is not a possibility without making String class immutable. Some people, when well-known sources tell them that fire will burn them, don't put their hands in the fire. Similarly, String is used as an argument while loading the class. as the 1st point you have write string pool. an object whose internal state remains constant after it has been entirely created In this post we’ll see some of the reasons for this design decision. That’s why String objects are immutable. I do agree immutable has its advantages and makes it easier to develop but most of the developers forget the memory overhead immutable objects bring in to the GC, when we have a immutable hashmap and when its changed, all the references has to recreated and redone for the new variable when we do this multiple times it puts an overhead on the GC and leads to stop the world GC which slows down the programme significantly. It shows that the strings are immutable. once we create a String object its data cannot be modified. At that time change in the string may result in loading … © Copyright 2011-2018 www.javatpoint.com. It’s a very popular interview question because the string is one of the most used classes in Java programming language. We can’t modify the state of an immutable object and if we try to modify it then it creates a new object. think of a port number in a property map). Java can have a string pool because strings are immutable. It means Strings were immutable that’s why java is still around in the game. Immutable String in Java. //here will cause problem, if s is changed before this by using other references. And don't forget - not only are Strings immutable. Why string is immutable in Java? These are some more reasons of making String immutable: Let's understand the concept of immutable through an example. All String literals are added to String pool by JVM. The string is made final to not allow others to extend it and destroy its immutability. ==== 3.1. As we know String uses the string constant pool for the memory location. If any one of them changes the value for others, this will be affected as well. This question has been asked in a number of interviews in the past and is still being asked. In your example, “foo” and “bar” are the immutable string objects, whereas foo and bar are the references to these string object.Fortunately, we can swap a value with another one, for a given reference ! 1. JavaTpoint offers college campus training on Core Java, Advance Java, .Net, Android, Hadoop, PHP, Web Technology and Python. Java String class is immutable which means once a String object is created it cannot be changed. Being immutable guarantees that hashcode will always be the same so that it can be cashed without worrying about the changes.That means, there is no need to calculate hashcode every time it is used. This way Java Runtime frees a lot of heap space because different String variables can refer to the same string variable in the pool. This eliminates the requirements of doing synchronization. The string is immutable means that we cannot change the object itself, but we can change the reference to the object. i.e. For example, in a HashMap or HashSet. i.e. it explain because to implement string pooling concept they have made string as immutable. The string is Immutable in Java: In this post, we are going to understand another important concept. 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