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   • Instance variable in Java Spring Bean

     Top Answer

     Answered Aug 04, 2013 · 6 votes

     I will try to address your questions separately.

     I used this variable abc in the methods of the beans and when they are reached by multiple threads will it damage the consistency of data each thread?

     The short answer to this question is yes. If you wrote a different value for abc in one Thread it may or may not be seen from another thread. This is the reason the volatile keyword was introduced.

     I you want to have mutable singleton beans in Spring then you need be careful with synchronization and use of volatile.

     The data will not be "corrupted" because, as you point out, String is immutable. But one thread may not see that another has changed the value of abc.

     So you have a variable abc;

     • abc = "Hi."
     • thread 1 reads abc as "Hi.".
     • thread 1 changes abc by writing to the reference: abc="Hello."
     • thread 2 reads abc, it is unclear whether abc reads "Hi." or "Hello.".

     I make the String abc variable to ThreadLocal object to provide each thread holds their own abc variable

     ThreadLocal is used to have each thread be given a different instance of a variable. This is often used to tying state to a thread in a web server as web servers use a thread pre request model.

     Tomcat 7 does not fix ThreadLocal leak issues. If you do not remove the variable you have set from a thread then it will cause a leak. Or even worse a request will get items from the context of another request. This happens when a thread is checked into the pool with context left in its ThreadLocal and then is checked out by another request.

     Tomcat 7 tires to detect these issues and swap out threads to drop their ThreadLocal variables. This is expensive and can be avoided by using ThreadLocal properly.

     You need to clear ThreadLocal variables in a servlet filter.

     So:

     If you have a variable abc that you want to write to in one thread and for that change not to been seen in other threads then you can use a ThreadLocal, but you need to be very careful to clear state after each request.

     If you have a variable abc that yo want to write to in one thread and for that change to be seen in other threads then you can use a singleton bean with a volatile variable.

     Check all answers on Stack Overflow

     1/5

   • Instance set in Java?

     Top Answer

     Answered Sep 05, 2011 · 13 votes

     There is no direct "instance set" in the JRE.

     But there is an IdentityHashMap

     , which implements a "instance map" according to your terminology.

     And there is a method called Collections.newSetFromMap()

     which can create a Set from an arbitrary Map implementation.

     So you can easily build your own instance set like this:

     Set<MyType> instanceSet = Collections.newSetFromMap(new IdentityHashMap<MyType,Boolean>());-

     Check all answers on Stack Overflow

     2/5

   • Instance methods in java

     Top Answer

     Answered Sep 26, 2017 · 1 votes

     There only needs to be one copy of instance methods in memory. When an instance method is called there will be a "this" variable implicitly included in the stack. The "this" variable allows the instance method to access the instance variables for the object instance that called it.

     Classes, including their methods, would typically end up in the long lived heap as it is uncommon for them to be garbage collected.

     Check all answers on Stack Overflow

     3/5

   • Instance Methods in Java

     Instance Methods are the group of codes that performs a particular task. Sometimes the program grows in size, and we want to separate the logic of the main method from other methods. A  method is a function written inside the class. Since java is an object-oriented programming language, we need to write a method inside some classes. 

     The important points regarding instance variables are:

     • Instance methods can access instance variables and instance methods directly and undeviatingly.
     • Instance methods can access static variables and static methods directly.

     Instance Method without parameter 

     Syntax:

     modifier return_type method_name( ){ method body ;}

     • modifier: It defines the access type of the method, and it is optional to use.
     • return_type: Method may return a value. Ex:- int, void, String, char, float, etc.

     Check all answers on Geeksforgeeks

     4/5

   • Also try

     instance in java programming	class vs instance in java
     difference between object and instance in java	static vs instance in java
     how to create a singleton instance in java	create class instance in java
     meaning of instance in java	create an instance in java

     5/5

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2. www.javatpoint.com › what-is-an-instance-in-javaWhat is an Instance in Java - Javatpoint

   www.javatpoint.com › what-is-an-instance-in-java

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   An object is an instance of a class, and in the Java programming language, instances are fundamental. In this post, we'll examine what a Java instance is and how classes and objects connect to it. A class is used as a blueprint or template for constructing objects in Java.

3. www.geeksforgeeks.org › difference-between-object-and-instance-in-javaDifference Between Object and Instance in Java - GeeksforGeeks

   www.geeksforgeeks.org › difference-between-object-and-instance-in-java

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   Oct 24, 2023 · Difference Between Object and Instance in Java. The object is an instance of a class. A class is like a blueprint or template that defines the properties and behavior of objects. When we create an object we are creating an instance of that class.

4. stackoverflow.com › questions › 5126082oop - What exactly is an instance in Java? - Stack Overflow

   stackoverflow.com › questions › 5126082

   Feb 26, 2011 · Objects, which are also called instances, are self-contained elements of a program with related features and data. For the most part, you use the class merely to create instances and then work with those instances. -Definition taken from the book "Sams Teach Yourself Java in 21 days".

5. www.geeksforgeeks.org › instance-methods-in-javaInstance Methods in Java - GeeksforGeeks

   www.geeksforgeeks.org › instance-methods-in-java

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   Nov 10, 2021 · There are two types of Instance methods in Java: Accessor Method (Getters) Mutator Method (Setters) The accessor method is used to make the code more secure and increase its protection level, accessor is also known as a getter.

6. stackoverflow.com › questions › 2885385What is the difference between an Instance and an Object?

   stackoverflow.com › questions › 2885385

   May 21, 2010 · An instance is an object but associated with a type, as in this method accepts Foo instances, or you can not put Animal instances in an instance of a List of Vehicles. object s for example have locks associated with them, not instance s, whereas instance s have methods.

7. stackoverflow.com › questions › 20461907java - what is meaning of instance in programming? - Stack...

   stackoverflow.com › questions › 20461907

   Dec 9, 2021 · Here is a pretty standard definition: An instance, in object-oriented programming (OOP), is a specific realization of any object. An object may be varied in a number of ways. Each realized variation of that object is an instance. The creation of a realized instance is called instantiation.

8. ioflood.com › blog › instance-in-javaWhat is an ‘Instance’ in Java? | Guide to Creating Objects

   ioflood.com › blog › instance-in-java

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   Nov 7, 2023 · In this comprehensive guide, we’ve delved into the concept of instances in Java, exploring their creation, usage, and related concepts. We’ve clarified what an instance in Java is, how it functions as an object created from a class, and how to create and manipulate these instances.

9. www.geeksforgeeks.org › classes-objects-javaClasses and Objects in Java - GeeksforGeeks

   www.geeksforgeeks.org › classes-objects-java

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   Sep 3, 2024 · An object in Java is a basic unit of Object-Oriented Programming and represents real-life entities. Objects are the instances of a class that are created to use the attributes and methods of a class. A typical Java program creates many objects, which as you know, interact by invoking methods. An object consists of :

10. beginnersbook.com › 2023 › 03Instance Variables in Java – Definition and Usage - BeginnersBook

    beginnersbook.com › 2023 › 03

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    Jan 1, 2024 · In Java, an instance variable is a variable that belongs to an instance of a class, rather than to the class itself. An instance variable is declared within a class, but outside of any method, and is defined for each object or instance of the class.

11. math.hws.edu › javanotes › c5Objects, Instance Methods, and Instance Variables - Hobart and...

    math.hws.edu › javanotes › c5

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    An object that is created using a class is said to be an instance of that class. We will sometimes say that the object belongs to the class. The variables that the object contains are called instance variables. The methods (that is, subroutines) that the object contains are called instance methods.