The equals() and hashCode() methods are very important for all objects in Java. In this tutorial, I will present to you all the basic knowledge about these two methods. By default, these methods are defined in Object objects, which are the parent objects of all… Read More
This method was introduced from Java 9. Here we have two overload methods delayedExecutor(), the first method has the following syntax:
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static Executor delayedExecutor(long delay, TimeUnit unit) |
This method returns an Executor object from the default Executor object that the CompletableFuture object uses to execute the task, after the delay.… Read More
This method was introduced from Java 9.
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CompletableFuture<T> completeOnTimeout(T value, long timeout, TimeUnit unit) |
This method is used to: if after a timeout period our task is still unfinished, instead of throwing out the TimeoutException exception like the orTimeout() method, our code will return the value that we passed in this method.… Read More
This method was introduced from Java 9.
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CompletableFuture<T> orTimeout(long timeout, TimeUnit unit) |
This method is used to specify that if our task does not complete within a certain period of time, the program will stop and be TimeoutException. In the following example, I want to calculate the sum of… Read More
In SQL, the GROUP BY statement returns the set of records having the same value in particular criteria. For example, you have a table that contains student information, each student coming from a different country. Use the GROUP BY statement according to national criteria, you… Read More
In the previous tutorial, I introduced to you all about the Future object in Java and I also told you that when using the get() method of the Future object, our program will be blocked until when all the tasks completed. To solve this blocking… Read More
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
