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There can be times when it's useful to have values that are shared across all instances of a particular class. Static fields and static constants enable this type of sharing by belonging to the class and not to the actual objects.
- Java Custom Serialization. In most of cases, when you will customize java serialization, you will be writing the fields one by one – in a sequence. Its most common way to override default java serialization process. Let’s say, we have one User object and we want to customize it’s serialization process.
- Java Serialization tutorial - Java object serialization is used to persist Java objects to a file, database, network, process or any other system. Serialization flattens objects into an ordered, or serialized stream of bytes. The ordered stream of bytes can then be read at a later time, or in another environment, to recreate the original objects.
- What is Java Serialization, What is Deserialization, Only classes which implement Serializable can be serialized, Why Serializable is not implemented by Object, The transient and static fields do not get serialized, What is serialVersionUID and Why should we declare it, Customizing Serialization and Deserialization with writeObject and readObject methods, Stopping Serialization.
Investintech able2extract pdf converter 10. A static method can be marked transient which would normally be redundant, but you could use this to highlight static fields you don't want to serialize. You can call this method from your writeObject to save you having to do this for every field.
The Static Modifier
Normally fields and methods defined in a class can be used only when an object of that class type has been created. For example, consider a simple Item class that keeps track of goods in a store:
To be able to use the getItemName() method, we must first create an Item object, in this case, catFood:
However, if the static modifier is included in a field or method declaration, no instance of the class is required in order to use the field or method — they are associated with the class and not an individual object. If you look back at the above example, you will see that the static modifier is already being used in the main method declaration:
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The main method is a static method that does not require an object to exist before it can be called. As main() is the starting point for any Java application, there are in fact no objects already in existence to call it. You could, if you felt like having a program that continually calls itself, do this:
Not very useful, but notice how the main() method can be called without an instance of a StaticExample class.
What Is a Static Field?
Static fields are also known as class fields. They are simply fields that have the static modifier in their declarations. For example, let's go back to the Item class and add a static field:
The fields itemId and itemName are normal non-static fields. When an instance of an Item class is created, these fields will have values that are held inside that object. If another Item object is created, it too will have itemId and itemName fields for storing values.
The uniqueId static field, however, holds a value that will be the same across all Item objects. If there are 100 Item objects, there will be 100 instances of the itemId and itemName fields, but only one uniqueId static field.
In the above example, uniqueId is used to give each Item object a unique number. This is easy to do if every Item object that is created takes the current value in the uniqueId static field and then increments it by one. The use of a static field means that each object does not need to know about the other objects to get a unique id. This could be useful if you wanted to know the order in which the Item objects were created.
What Is a Static Constant?
Static Variables In Java
Static constants are exactly like static fields except that their values cannot be changed. In the field declaration, the final and static modifiers are both used. For example, perhaps the Item class should impose a restriction on the length of the itemName. We could create a static constant maxItemNameLength:
As with static fields, static constants are associated with the class rather than an individual object:
There are two important things to notice about the maxItemNameLength static constant:
- It is declared as a public field. Generally it's a bad idea to make a field public in any class you design but in this case, it doesn't matter. The value of the constant cannot be changed.
- The static constant is used from the class name Item, not an Item object.
Java Serialization Static Fields Test
Static constants can be seen throughout the Java API. Free random number generator. For example, the integer wrapper class has two that store the maximum and minimum values an int data type can have: