Why string is immutable in java

Java Strings are immutable by default. The immutability of Strings helps in providing features such as caching, security, fast performance and better memory utilization. This tutorial discusses how the immutability of Strings helps in achieving these features. 1. What is an Immutable Class? Let us start with an object whose state is guaranteed to remain unchanged over its entire lifetime. It means that the object’s state, once initialized, can never be changed anyway. Java also has immutable classes, which are primarily String and 2. Strings in Action When we create a String, a String object is searched in the String str1 = "value"; String str2 = "value"; String str3 = "value"; The above program creates 3 String type variables, all pointing to the same object in the spring pool area. All future Strings with content “value” will point to the same object in the heap and thus save the memory. 3. Advantages of Immutable Strings Let us now understand how the above-discussed immutability helps in runtime. 3.1. Application and Data Security The first and undeniably most important reason is security. Well, it is not only about our application but even for JDK itself. Java class loading mechanism works on class names passed as parameters, then these classes are searched in the classpath. In the following program, we are loading the SQL server driver by its class name. Imagine for a moment, Strings were mutable, then a bad actor could have changed the driver name, loaded a bad drive...

In java, string objects are immutable because String objects are cached in String pool. 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. JVM has string pool which shared between multiple clients so there is always risk of modification by one client can affect all other clients.It is very important and popular question of java interview, why String is immutable in Java? it is one of the most frequently asked String Interview questions in Java, String class very important class of java and there lots of uses, string class has many benefits because immutable object. String Pooling requirement Suppose one client has a string object with value “java” if this client changes the value of String “java” to “JAVA” then all other clients will also see that changed value. As we know JVM provide String pool system to cache the string value for performance reason this risk was avoided by making String class Immutable. Popular Tutorials • Spring Tutorial • Spring MVC Web Tutorial • Spring Boot Tutorial • Spring Security Tutorial • Spring AOP Tutorial • Spring JDBC Tutorial • Spring HATEOAS • Microservices with Spring Boot • REST Webservice • Core Java • Hibernate Tutorial • Spring Batch The following code will create only one string object in the heap. String str1 = "java"; String str2 = "java"; Here is how it looks: If a string is not immutable, changing the string with one refe...

Consider the following example. String str = new String(); str = "Hello"; System.out.println(str); //Prints Hello str = "Help!"; System.out.println(str); //Prints Help! Now, in Java, String objects are immutable. Then how come the object str can be assigned value "Help!". Isn't this contradicting the immutability of strings in Java? Can anybody please explain me the exact concept of immutability? Edit: Ok. I am now getting it, but just one follow-up question. What about the following code: String str = "Mississippi"; System.out.println(str); // prints Mississippi str = str.replace("i", "!"); System.out.println(str); // prints M!ss!ss!pp! Does this mean that two objects are created again ("Mississippi" and "M!ss!ss!pp!") and the reference str points to a different object after replace() method? str is not an object, it's a reference to an object. "Hello" and "Help!" are two distinct String objects. Thus, str points to a string. You can change what it points to, but not that which it points at. Take this code, for example: String s1 = "Hello"; String s2 = s1; // s1 and s2 now point at the same string - "Hello" Now, there is nothing 1 we could do to s1 that would affect the value of s2. They refer to the same object - the string "Hello" - but that object is immutable and thus cannot be altered. If we do something like this: s1 = "Help!"; System.out.println(s2); // still prints "Hello" Here we see the difference between mutating an object, and changing a reference. s2 still po...

Mutable and Immutable in Java Java is an object-oriented programming language. As it is an object-oriented programming language, it's all methods and mechanism revolves around the objects. One object-based concept is mutable and In this section, we will discuss mutable and immutable objects in Java. Further, we will see the difference between them. What are Mutable Objects The mutable objects are objects whose value can be changed after initialization. We can change the object's values, such as field and states, after the object is created. For example, When we made a change in existing mutable objects, no new object will be created; instead, it will alter the value of the existing object. These object's classes provide methods to make changes in it. The Getters and Setters ( get() and set() methods ) are available in mutable objects. The Mutable object may or may not be thread-safe. What are Immutable Objects The immutable objects are objects whose value can not be changed after initialization. We can not change anything once the object is created. For example, primitive objects such as all In a nutshell, immutable means unmodified or unchangeable. Once the immutable objects are created, its object values and state can not be changed. Only Getters ( get() method) are available not Setters ( set() method) for immutable objects. Let's see how to create classes for mutable and immutable objects. How to Create a Mutable Class The following two things are essential for creatin...

Why String is immutable in Java is one of the popular interview questions. The string is one of the most used classes in any programming language. We know that String is immutable and final in Java. Java runtime maintains a Let’s look at some of the benefits of String immutability, that will help in understanding why String is immutable in Java. • • If String is not immutable then it would cause a severe security threat to the application. For example, database username, password are passed as String to get database connection and in • Since String is immutable, it is safe for • Strings are used in java.sql.Connection class but the referenced value is changed to myhacked.Connection class that can do unwanted things to your database. • Since String is immutable, its hashcode is cached at the time of creation and it doesn’t need to be calculated again. This makes it a great candidate for the key in a Map and its processing is faster than other HashMap key objects. This is why String is the most widely used as HashMap keys. Above are some of the reasons I could think of that shows benefits of String immutability. It’s a great feature of the You can checkout more Java String examples from our Refer the below code : public class StringImmutable_Test_1_0 This gives me output as follows --> s1 and s2 has same reference s1 and s3 doesn’t have same reference Why this is giving me such result although string is immutable ? - Nilakshi Patil String s1 = “ABC”;-- This goes to pool dir...

As per my knowledge, a mutable string can be changed, and an immutable string cannot be changed. Here I want to change the value of String like this, String str="Good"; str=str+" Morning"; and other way is, StringBuffer str= new StringBuffer("Good"); str.append(" Morning"); In both the cases I am trying to alter the value of str. Can anyone tell me, what is difference in both case and give me clear picture of mutable and immutable objects. Case 1: String str = "Good"; str = str + " Morning"; In the above code you create 3 String Objects. • "Good" it goes into the String Pool. • " Morning" it goes into the String Pool as well. • "Good Morning" created by concatenating "Good" and " Morning". This guy goes on the Heap. Note: Strings are always immutable. There is no, such thing as a mutable String. str is just a reference which eventually points to "Good Morning". You are actually, not working on 1 object. you have 3 distinct String Objects. Case 2: StringBuffer str = new StringBuffer("Good"); str.append(" Morning"); StringBuffer contains an array of characters. It is not same as a String. The above code adds characters to the existing array. Effectively, StringBuffer is mutable, its String representation isn't. • Mutable :- Changeable • Immutable :- Unchangeable String in Java is immutable. However what does it mean to be mutable in programming context is the first question. Consider following class, public class Dimension ); String str5 = str1 + str2; str1 = "Hi !"; // ... ...

String str1 = "w3spoint" ; String str2 = "w3spoint" ; String str1 = "w3spoint"; String str2 = "w3spoint"; When the 1st statement executes, Java will check string pool and it will create one “w3spoint” literal as there is no such string literal present in the string pool. When 2nd statement executes, Java again checks whether “w3spoint” present in the string pool or not. As it is present because of 1st statement, no more literal will be created for “w3spoint” and both str1 and str2 reference variable will point to same literal. But if we write the code like: String str1 = "w3spoint" ; String str2 = "w3spoint" ; str1. concat ( ".com" ) ; String str1 = "w3spoint"; String str2 = "w3spoint"; str1.concat(".com"); Then 3rd statement will not modify “w3spoint” literal, Java will create one more literal with modified value i.e. “w3spoint.com”. Now str1 will point to “w3spoint.com” and str2 will point to “w3spoint”. As you can see that existing literals will not be modified hence we can say that string objects are immutable or final. Advantages of immutable strings • Java Runtime saves a lot of heap space because multiple string references can point to the same String literal. • Immutable objects are thread safe. • HashCode of immutable object is cached at object creation time. There is no need to calculate it again and again, which results into high performance. Immutability is the reason because of which String preferred as HashMap key. Java interview questions on String Handling ...

Java String Java Regex Exception Handling Java Inner classes Java Multithreading Java I/O Java Networking Java AWT & Events Java Swing JavaFX Java Applet Java Reflection Java Date Java Conversion Java Collection Java JDBC Java Misc Java New Features RMI Internationalization Interview Questions Java MCQ Why String is Immutable or Final in Java In object-oriented programming, the immutable string or objects that cannot be modified once it is created. But we can only change the reference to the object. We restrict to change the object itself. The String is immutable in The String objects are cached in the String pool, and it makes the These are some more reasons of making String immutable: • The String pool cannot be possible if String is not immutable in Java. A lot of heap space is saved by • If we don't make the String immutable, it will pose a serious security threat to the application. For example, database usernames, passwords are passed as strings to receive database connections. The • The String is safe for multithreading because of its immutableness. Different threads can access a single "String instance". It removes the synchronization for thread safety because we make strings thread-safe implicitly. • Immutability gives the security of loading the correct class by Classloader. 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 da...

Closed 7 years ago. How can this be if I can create a String, giving it a value. Then, I can simply overwrite its value like this: String a="abc"; a="def"; How is it possible that I can change the value of a? I must be missing something here. I understand that Strings literals are used whenever creating a String object, rather than creating a new instance of String every time Please help, thanks. No worries, but please do try googling next time (or, if you did, let us know what you searched for and why it didn't answer your question). I didn't remember the marked duplicate offhand, but a search for "java string immutable" had several highly relevant answers (including the one I marked this as a duplicate of). Your not changing its value you are creating a new String. Technically your variable changes its value (memory location its pointing to) to reference a new String object but it is pointing to the new String object not the same String object. You aren't actually changing the value of the original String object you are just referencing a new String so while the value of your variable does change you aren't actually changing the original String object...Hope that makes sense. String a="abc";//creating string literal object a="def"; You are actually changing the reference of a to a new object created by the String literal "def". String is immutable means that you cannot change the object itself, but you can change the reference to the object. Changing an object means to u...