In Java 8, the Elvis operator (often written as ?: in Groovy and Kotlin) is not available as a built-in feature. However, we can achieve similar functionality using various techniques. Below are multiple methods to simulate the Elvis operator in Java 8+.
1. Understanding the Elvis Operator
The Elvis operator is a shorthand conditional operator found in languages like Groovy and Kotlin. It provides a concise way to handle null values by returning a default value if the original value is null.
For instance, in Kotlin, the following code snippet uses the Elvis operator:
val name = person?.name ?: "Unknown"
This code assigns a value to the name variable. If person is not null and has a name property, that name is assigned. Otherwise, “Unknown” becomes the default value.
2. Implementing the Elvis Operator in Java
2.1 Using Ternary Operator
The ternary operator (?:) is a straightforward way to implement the Elvis operator in Java. It uses a simple conditional expression (value != null) ? value : "default value" to check if value is not null and return it; otherwise, it returns the default value.
ElvisOperatorWithTenaryExample.java
public class ElvisOperatorWithTenaryExample {
public static String getName(Person person) {
return person != null ? person.getName() : "Unknown";
}
public static void main(String[] args) {
Person personWithName = new Person();
personWithName.setName("Alice");
String name = getName(personWithName);
System.out.println(name); // Output: Alice
Person personWithoutName = null;
String defaultName = getName(personWithoutName);
System.out.println(defaultName); // Output: Unknown
}
}
class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
2.2 Using Optional Class
Java 8 introduced the Optional class, which offers a more functional approach to handling the presence or absence of a value.
ElvisOperatorWithOptionalClass.java
public class ElvisOperatorWithOptinalClass {
public static String getName(Person person) {
return Optional.ofNullable(person)
.map(Person::getName)
.orElse("Unknown");
}
public static void main(String[] args) {
Person personWithName = new Person();
personWithName.setName("Alexander");
String name = getName(personWithName);
System.out.println(name); // Output: Alexander
Person personWithoutName = null;
String defaultName = getName(personWithoutName);
System.out.println(defaultName); // Output: Unknown
}
}
class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
In this example:
Optional.ofNullable(person)creates anOptionalobject that can be null.map(Person::getName)applies thegetNamemethod reference to the value inside theOptional(if it exists).orElse("Unknown")returns the default value “Unknown” if theOptionalis empty (meaningpersonwas null).
2.3 Using a Custom Method
We can create a custom Elvis method that mimics the Elvis operator’s behaviour.
ElvisOperatorWithCustomMethod.java
public class ElvisOperatorWithCustomMethod {
public static <T> T elvisOperator(T value, T defaultValue) {
return (value != null) ? value : defaultValue;
}
public static String getName(Person person) {
return elvisOperator(person.getName(), "UnKnown");
}
public static void main(String[] args) {
Person personWithName = new Person();
personWithName.setName("Alice");
String result = getName(personWithName);
System.out.println(result);
Person personWithoutName = new Person();
personWithoutName.setName(null);
String defaultName = getName(personWithoutName);
System.out.println(defaultName);
}
}
Explanation:
- The
elvisOperatormethod is a generic method that takes two arguments: the value to check and the default value. - It returns the value if it’s not null, otherwise, it returns the default value.
Output:
2.4 Using Objects.requireNonNullElse() (Java 9+)
The Objects.requireNonNullElse() method can be used to achieve the Elvis operator functionality directly and concisely. The Objects.requireNonNullElse() method handles null values by providing a default value if the given value is null. This method checks if the first argument is null and returns the second argument as the default value if it is.
ElvisOperatorWithObjectsNonNull.java
public class ElvisOperatorWithObjectsNonNull {
public static void main(String[] args) {
// Example usage
Person personWithNullName = new Person(null);
Person personWithName = new Person("John");
// Using Objects.requireNonNullElse to provide default name
String name1 = Objects.requireNonNullElse(personWithNullName.getName(), "Default Name");
String name2 = Objects.requireNonNullElse(personWithName.getName(), "Default Name");
System.out.println(name1); // Output: Default Name
System.out.println(name2); // Output: John
}
}
3. Conclusion
In this article, we explored various methods to implement the Elvis operator in Java, from using the simple ternary operator to leveraging more advanced techniques such as Optional and utility methods. Each method has its own advantages and can be chosen based on specific requirements and coding style preferences. The ternary operator is straightforward and effective for simple cases, while Optional provides a more functional and declarative approach. Utility methods offer reusability and type safety.
4. Download the Source Code
This was an article on Java 8 Elvis operator implementation.
You can download the full source code of this example here: Java 8 Elvis operator implementation
