The document outlines the features and functionalities of record classes in Java, introduced for creating simple data carriers. It explains automatic generation of equals, hashcode, tostring methods and constructors, as well as details on adding static members, instance methods, and the implications of serialization. Key limitations include the inability to extend record classes and include native methods.

1. Record Classes in Java
Haim Michael
March 7th
, 2023
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2. © 2008 Haim Michael 20230307
What is a Record Class?
 When declaring a record class we declare a sequence of
fields. The equals, hashCode, and toString are
automatically generated. Each field we declare automatically
becomes a final private field. In order to allow us getting
the values of those fields, for each field a method with the
same name is auto generated. In addition, a simple
constructor is automatically generated in accordance with the
declared fields.

3. © 2008 Haim Michael 20230307
What is a Record Class?
public record Book(int id, String title, String author) {}

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Simple Data Carrier
 The purpose of the record class is to serve as a simple data
carrier. For that reason, the fields automatically become final.

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Explicit Constructor
 When declaring a record we can declare a constructor that
will take the place of auto generated one.
public record Book(int id, String title, String author)
{
public Book(int id, String title, String author)
{
this.id = id;
this.title = title;
this.author = author;
}
}

6. © 2008 Haim Michael 20230307
Explicit Constructor
 When declaring a constructor we can avoid the tedious repeat
of all components.
public record Book(int id, String title, String author) {
public Book {
if(id<0)
throw new UnsupportedOperationException(
"id cannot be negative");
}
}
The assignment of the arguments take place
automatically. Referring the this keyword is
impossible.

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Implementing The Accessors
 We can implement the access methods by ourselves. We
should make sure the type of their returned value is the same
and we should make sure they are with the same
accessibility.
public record Book(int id, String title, String author) {
public int id() {
System.out.println(“id was retrieved”);
return id;
}
}

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The hashCode Method
 We can implement it by ourselves. Our implementation will
take the place of the auto generated one.

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The toString Method
 We can implement it by ourselves. Our implementation will
take the place of the auto generated one.

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The equals Method
 We can implement it by ourselves. Our implementation will
take the place of the auto generated one.

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Static Members
 We can add static members to the record class we declare.
We can add static variables, static methods, and static blocks.

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Instance Members
 We cannot add instance variables to the definition of our new
record class. It is certainly possible to add the definition of
instance methods.

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Nested Classes
 We can include in our record the definition of nested classes,
nested interfaces, and nested records. The new nested types
cannot be instance members.

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Native Methods
 It isn't possible to include within the definition of a new record
the definition of a native method.

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Final Class
 The record class we define is automatically final. We cannot
extend a record class.

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Local Record Class
 When we define a record class within the scope of a method
we get a local record class.

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Serialization
 We can serialize and deserialize instances of record classes.
We cannot customize the serialization by providing our
versions for methods, such as writeObject, readObject,
and readObjectNoData.

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The java.lang.Record Class
 Every record class we define implicitly extends the
java.lang.Record class.

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Questions & Answers
Thanks for Your Time!
Haim Michael
haim.michael@lifemichael.com
+972+3+3726013 ext:700
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michae
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