Replace with null in java

Working with Nulls in Java

In this article, we will learn some ways to deal with Null value in Java. Let’s get started.

Table of contents

Working with Reference types and Nulls

1. Null and Reference types In the conference, in 2009, Sir Charles Antony Richard Hoare apologized for introducing null references in the programming language Algol Wz in 1965.

 I call it my billion-dollar mistake. It was the invention of the null reference in 1965. [. ] This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years. 

• Optional data Null is useful concept, it allows modeling optional data. For example, for certain the type of books, ISBN numbers are optional.
• Unknown data Null also allow us to model data that hasn’t been entered yet, but it will be available at some point. For example, a book record can be created before the book’s finished and the exact number of pages is known.
• Eager deinitialization Null can be used for either the initialization, too. For example, if a class manages its own memory, when an element is free, it should be noted out to avoid memory leaks.

From a technical point of view, null is a value that indicates that our reference does not refer to an object.

In assignment statement, it has three parts. The first part declares a reference variable. The second part creates an object of the type book telling the JVM to allocates space for a new book object in memory. Finally, the third part assigns the book object to a reference variable.

We also cannot meet the object creation, and in this case, the reference Book would refer to nothing at all because for all reference types, null is the default value. In other words, these two statements are equivalent.

 Book book; Book book = null; 

–> Nulls can be completely avoided in Java.

 public boolean isBookReadyForPublication(Book book)  assert book != null : "Book is null"; // . > 

 public boolean isBookReadyForPublication(Book book)  if (book != null)  // null != book // . > else  // . > > 

 public boolean isBookReadyForPublication(Book book)  Objects.requireNonNull(book, "Book is null"); // or if (Objects.isNull(book))  // Objects.nonNull(book) // book object is null > else  // do something with book object > > 

 public boolean isBookReadyForPublication(Book book)  try  // use book object > catch(NullPointerException ex)  // book object was null > > 

Use try/catch version will have better performance because there’s no checking for null. Exceptions may be a big cheaper in terms of performance. But using exception in this way, it’s about practice because it leads to go, hard to understand.

• Best practices for data that we don’t control We can clarify the data that flows through an application in two types.
  • Given problem Below is an image that describes that our flow’s data in application. The data that we do not control is the data that is sent from Client to Server. It means that data from Presentation layer to Service layer.

  For parts of the application where we don’t have control of the data:

  • Document our public API It means that every class, interface, constructor, methods should have Java doc comments. For methods describe the contract:
    • preconditions
    • postconditions
    • parameters
    • return values

    

    • At the beginning of the method, use the general principle fail-fast.
    • If an invalid parameter value is passed to the method and the method checks for this before continuing its execution, it can take appropriate action. There are two options for this case:
      • Replace the null value with some default value such as using empty string, a negative value or an empty List. This solution is not always the right choice. It can cause the other errors.
      • Throw exceptions to indicate that an invalid value has been received. We can choose one of the NullPointerException or IllegalArgumentException and use it consistently. For example:

       public boolean isBookReadyForPublication(Book book)  Objects.requireNonNull(book, "Book is null"); Objects.requireNonNull(book.getAuthor(), "Author is null"); Objects.requireNonNull(book.getTitle(), "Title is null"); // business logic of this method // . > 

       public boolean publishBook(Book book, Date publicationDate)  // . > 

      In an above code, if the publicationDate variable is optional, instead of doing like the above code, it’s better to have the overloaded methods like the below.

       public boolean publishBook(Book book)  // . > 

       public HashSetEdition> getBookEditions()  return book.hasEditions() ? null : new HashSetEdition>(book.getEditions()); > 

      If null means that something could not be found, instead of using null value, we can return an empty collections.

       public HashSetEdition> getBookEditions()  return book.hasEditions() ? new HashSetEdition>() : new HashSetEdition>(book.getEditions()); > 

      Checking for Null using annotations

       ```java public class BookService < @NonNull private Integer defaultBookId; private void setDefaultBookId(@NonNull Integer id) < this.defaultBookId = id; >@NonNull private Integer getDefaultBookId() < return this.defaultBookId; >> 

      This annotation allows our object can be null. For example: «`java public interface BookRepository extends JpaRepository

      

    • @NonNullApi In order to configure this annotation, we have to define it in the package-info.java file of the root directory package.
    • @NonNullFields
  • Bean Validation Annotations Bean validation is the standard validation of specification, is defined by JSR 303 for its first version and JSR 380 for its second version. Some annotations that we need to know:
    • @NotNull
    • @Size
    • @Min/@Max
    • @PositiveOrZero

    Hibernate validator is the reference implementation of the specification, hibernate is associated with the persistent layer and that can be a source of confusion, especially about two things:

    • Does Hibernate Validator only validate objects of the domain model? No, it validates objects in all layers.
    • Are @NotNull and @Column(nullable = false) equivalent? No, the @Column annotation is part of the JPA specification. However, it doesn’t perform any validation if we annotate fields. If Hibernate creates the table, it adds a not null constraint to the database column, the database is the one that checks if the value is not null when we insert or update a record. @NotNull is a part of the Bean Validation specification. It triggers a validation during an update or persist lifecycle event. It validates at the applicaltion level. If it fail, Hibernate will not execute any SQL statement.
    • @NonNull annnotation for parameters of methods and constructors. It also used with the @Data annnotation

    To choose an annotation library, consider:

    • At what point the null check is performed.
    • Where we can use the annotations.
    • Tool and language interoperability and compability.

    Using the Null Object pattern

    In order to use Null Object pattern, we can refer the article Null Object pattern.

    So, instead of using a null reference to represent the absence of an object, it uses an object that implements the expected interface but does nothing, hiding the details from its collaborators.

    Some notes about Null Object pattern:

    • It’s not a kind of GoF patterns.
    • It was described in a article The Null Object pattern by Bobby Woolf. And later, it was published in the Pattern Languages of Program Design Vol.3.
    • The other names of this pattern are Active nothing, Stub.
    • The other pattern that has the same idea with this Null Object pattern is the Special pattern.

    Using Optional instead of Null

    Belows are some article we need to read:

    Wrapping up

    • Null is a value that indicates that a reference does not refer to an object.
    • The type of the literal value null is Null. That’s why use null with instanceof() will return false.
    • If we use null object, Java will throw a NullPointerException. To avoid a NullPointerException, developers traditionally use:
      • Assertions
      • If/else statements
      • Methods of the java.util.Objects class
      • And even try/catch blocks.

      It’s better to no overcomplicate things.

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      Replace null with Empty String in Java

      In this post, we will see how to replace null with empty String in java.

      Use String’s replace() method to replace null with empty String

      You can use String’s replace() method to replace null with empty String in java.

      As String is immutable in java, you need to assign the result either to new String or same String.

      String’s replace() method returns a string replacing all the CharSequence to CharSequence.
      Syntax of replace() method:

      Let’s understand with the help of example:

      Let’s say you have list of Strings which you are getting from database. If any String in the list is null, replace it with empty String.

      As you can see in output, we have replaced all null values in the list with empty String.
      str == null ? «» : str is ternary operator. It means if String is null return empty String else return same String.

      Further reading:

      Add Characters to String in Java

      Replace Space with Underscore in Java

      Print empty String rather than null in Java

      If you want to print empty String rather than null, then you can use ternary operator.

      That’s all about how to replace null with empty String in java.

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