As you all know, the Optional object is a generic object, its data type can be any object, and therefore, we can meet the case that its data type is also an Optional object, such as: Optional<Optional<String>>. To resolve this problem, Java introduces us to… Read More
This method will check whether an Optional object is not empty? If this object is empty, it returns false. For example:
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package com.huongdanjava.javaexample; import java.util.Optional; public class Example { public static void main(String[] args) { String s = new String("Khanh"); Optional<String> opt = Optional.ofNullable(s); System.out.println(opt.isPresent()); } } |
Result:
This method first will check whether our Optional object is empty or not? If not empty, convert its value to another value. Similar to the filter() method, this method returns an Optional object with a value after conversion. For example:
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package com.huongdanjava.javaexample; import java.util.Optional; public class Example { public static void main(String[] args) { String s = new String("Khanh"); Optional<String> opt = Optional.ofNullable(s); opt.map(x -> x.toLowerCase()) .filter(x -> x.contains("k")) .ifPresent(x -> System.out.println("Name: " + x)); } } |
In the above example,… Read More
This method first will check whether our Optional object is empty or not? If not, then continue to check whether its value meets a certain condition or not? If satisfied, it returns an Optional object containing this value, otherwise returns an empty Optional object. For… Read More
This method was introduced from Java 9. This method is similar to the ifPresent() method which I introduced in this tutorial, but here is a difference since we have one more Runnable parameter, so that in-case if the Optional object is empty, the object of the… Read More
This method is used to check whether an Optional object is empty or not? If not, then do the operations with this object, otherwise do not do anything. The parameter of this method is an object of the Consumer interface. You can see more about… Read More
The Optional object in Java has three methods with name start with or(). In this tutorial, we will together learn about them and what is the difference between them. First, I might mention the orElse() method. This method is used to return a default value in… Read More
This method is supported since Java 9. This method is used to create a new Stream object from an Optional object in Java. If the Optional object contains a value, this method will return the Stream object containing that value, otherwise, it returns an empty… Read More
In the previous tutorial, I introduced with you all about the Optional object in Java. In this tutorial, let’s find out some ways to initialize your Optional object in Java. OK … First, we can initialize an Optional object with the nulled reference variable. For… Read More
In the previous tutorial about NullPointerException in Java, I have presented to you some cases where NPE can occur and how to deal with them to avoid. From Java 8, we have another way to avoid NullPointerException, that will use the Optional object. What is… Read More
