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Here the question is why String is immutable in java? set.add(new String("c")); String pool is a special storage area in Method Area (). 27, Sep 18. To really answer this question we will have to ask the designers of the Java language because only they can answer this questions. String is immutable in Java. In object-oriented programming, the immutable string or objects that cannot be modified once it is created. If several references point to same String without even knowing it, it would be bad if one of the references modified that String value. This is more efficient. Why String is immutable in Java? think of a port number in a property map). All String literals are added to String pool by JVM. In this post we’ll see some of the reasons for this design decision. Java 8 Object Oriented Programming Programming. What is String immutability? Why String pool in Java Heap? i.e. The key benefits of keeping this class as immutable are caching, security, synchronization, and performance. String in java is a final class and immutable class, so it can’t be inherited, and we can’t alter the object. throw new SecurityException(); The reason of making string final is to destroy the immutability and to not allow others to extend it. If you search google for this question you will find people trying to answer this question. as well (e.g. Java 8 Object Oriented Programming Programming. Thus, String is immutable in nature. Why String is Final As discussed in How to Create an Immutable Class in Java, in order to make a class immutable we need to make sure no one extends our class and destroy its immutability. In Java Once we created string object we cannot change and modify its data or state. String pool is possible only because String is immutable in Java. We restrict to change the object itself. To make this concrete, consider the following program: HashSet set = new HashSet(); once we create a String object its data cannot be modified. Two reasons are important to say why Immutable String class is made in Java: 1. 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. Let's discuss how these things work. as the 1st point you have write string pool. The term Mutable means "can change" and Immutable means "cannot change". String class is immutable i.e. In every java interview definitely you will face Why String is Immutable in Java, Or can you list down few secret of String? Similarly, String is used as an argument while loading the class. In Java immutable objects are those whose data can’t be changed or modified (once modified). An Immutable Object means that the state of the Object cannot change after its creation. String string1 = "abcd"; Since cached String literals are shared between multiple clients there is always a risk, where one client's action would affect all another client. 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. 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. Why string is immutable in java? For example, suppose we have an instance where we try to load java.sql.Connection class but the changes in the referenced value to the myhacked.Connection class does unwanted things to our database. There are a number of factors that considered when the string was introduced in java. Why String is immutable in Java is one of the popular interview questions. Immutability gives the security of loading the correct class by Classloader. You can also refer http://java-journal.blogspot.in/2010/12/why-strings-in-java-are-immutable.html. If several references point to same String without even knowing it, it would be bad if one of the references modified that String value. Create Java String Using ” ” or Constructor? Another advantage is that strings in Python are considered as “elemental” as numbers. set.add(new String("a")); Java Object Oriented Programming Programming. The same reasoning you provided for String to be immutable applies to Integer etc. Since Strings are immutable there is no way contents of Strings can be changed because any change will produce new String. Immutable simply means unmodifiable or unchangeable means once string object is created its data or state can’t be changed but a new string object is created. Of curse, the example above is just for demonstration purpose and there is no value field in a real string class. 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”. Thus, with this article at OpenGenus, these are the reasons which answers the question "why String is immutable in Java".If you think there are some reasons then comment down in the discussion section given below. Why not Method? 1. The String objects are cached in the String pool, and it makes the String immutable. 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. Let’s see why String is immutable in java. Since string once created can’t be modified so the hashcode once calculated for any string can be cached and reused. I think String pool in Method Area, not in Heap. String is immutable in Java. 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. If any one of them changes the value for others, this will be affected as well. In java, string objects are immutable. How can immutable object be a thread safe!? The string is Immutable in Java because String objects are cached in the String pool. 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. Some people, when well-known sources tell them that fire will burn them, don't put their hands in the fire. Re: Why is String and Wrapper Classes are immutable in Java????? The string is one of the most used classes in any programming language. 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. 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(String a: set) Some people, being skeptical, will put their hands in the fire, get burned, and learn not to put their hands in the fire. The String is immutable in Java because of the security, synchronization and concurrency, caching, and class loading. Mutable strings could cause a security problem in Reflection too, as the parameters are strings. These are some more reasons of making String immutable: Let's understand the concept of immutable through an example. Why is String immutable in java? Immutable objects are those objects that can’t change after creation. And don't forget - not only are Strings immutable. Because immutable objects can not be changed, they can be shared among multiple threads freely. That is why string is immutable in java? Different threads can access a single "String instance". String pool is possible only because String is immutable in Java. In Java, Strings are immutable. So, there is always a risk, where action performs by one client affects all other clients. Class java.lang.String is also final. In general, strings are used to represent the vital details like database connection URLs, username passwords etc. “ Test ” can be changed and this can lead to a serious security threat in., their advantages why string is immutable in java how to create them, and once created can ’ t modify the state an! College campus training on Core Java, String objects are cached in String pool can not modified! Of String immutability with an example state ca n't be modified so the hashcode of String! 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