KnpCode
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Java, Spring, BigData, Web development tutorials with examples
KnpCode
2y ago
In this tutorial we’ll see what is React.Fragment and how to use it.
Table of contents
Why React Fragment
React Fragment Usage
Fragment short syntax
Key with Fragments
Why React Fragment
When you write a React component there is a constraint that the JSX expression the component will render should always be wrapped with in a single parent element. Which means trying to write a component as given below results in an error.
const HelloWorld = (props) => {
return (
<h2>{props.title}</h2>
<p>{props.message.greeting} {props.message.name}</p> ..read more
KnpCode
2y ago
The React useState hook is used to add state to your functional component. That way you can track the state in a component.
Table of contents
What does useState hook do
React useState hook example
Change state using previous state
Using useState with forms
Form example with multiple state hooks
Form example with Single state hook
What does useState hook do
When we say useState tracks the state in a functional component it means it can track the changes in the data in your component which may be any variable, object in the component. Any change in the data can be termed as the state chan ..read more
KnpCode
2y ago
In this tutorial you’ll see how to use Collectors.collectingAndThen() method with the help of some examples.
Collectors.collectingAndThen() method in Java Stream
As the name of the method itself suggests this method helps you to provide logic for two steps in a single method call.
1. How to collect stream elements.
2. What to do after collecting Stream elements.
Syntax of collectingAndThen() method is as given below-
Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)
Here parameters are-
downstream– A collector that is applied to stream ..read more
KnpCode
2y ago
In this tutorial you’ll learn how to use props on React components.
Table of contents
Why do we need props
React props example
Passing more than one value as props
Passing down data using props
Why do we need props
When you create a component in React you want it to be reusable, which involves calling the same component with different values just like methods where you can pass parameters. In simple terms ‘props’ are the arguments passed to the user-defined component. When you use your component as an element you can pass values to it as attributes. When React sees an element representing ..read more
KnpCode
2y ago
If you are starting to learn Reactjs and just created your first Hello World React app, you may be wondering what is the flow of the React app. Moreover, if you have used create-react-app to set up your project structure, you get a readymade default app and if you execute command npm start you can also view the application by going to URL- http://localhost:3000.
Again, if you are wondering how you got this display and what all happened underneath to get to this display on your browser then this article will help you in understanding the React app flow.
React project structure (create-react-ap ..read more
KnpCode
2y ago
Wrapper class in Java is a class whose object wraps a primitive type. When you need an object instead of a primitive type you can use Wrapper class to wrap the primitive type value in an object and use that object.
Wrapper classes in Java for primitive types
For all eight primitive data types there is a corresponding Wrapper class in Java.
Primitive Type
Wrapper class
boolean
Boolean
char
Character
byte
Byte
short
Short
int
Integer
long
Long
float
Float
double
Double
Out of these 8 wrapper classes 6 are numeric. All of the numeric wrapper classes are subclasses of the abs ..read more
KnpCode
2y ago
Node.js is a popular run time environment for executing JavaScript applications. If you are using popular JS frameworks like Angular, React then also it is required that you should have Node.js installed on your system. In this tutorial we’ll see how to download and install Node.js and NPM (Node Package Manager) on a Windows system.
Installing Node.js and NPM on windows
1. Downloading Node.js installer
You can download Node.js from this location- https://nodejs.org/en/download/
Once you are on the page select one of the two choices LTS or Current. Better to opt for LTS (Long Term Support) vers ..read more
KnpCode
2y ago
In this tutorial you will see how to write your first React program, a Hello World React application that gets you started with creating a Reactjs project and then writing code to display Hello World in a browser.
Table of contents
Create React App for Creating Reactjs project
Creating HelloWorld React application
Creating React component
React component as ES6 class
Create React App for Creating Reactjs project
create-react-app command provides an easy way to create a Reactjs project with default configuration.
You don’t need to install or configure tools like webpack or Babel yourself se ..read more
KnpCode
2y ago
In the tutorial Java Stream Collectors averagingInt(), averagingLong(), averagingDouble() we saw how Collectors class in Java Stream API provides methods like Collectors.averagingInt(), Collectors.averagingLong(), Collectors.averagingDouble() to get average of Stream on Integers, Long and Double respectively. Same way if you want to quickly add the stream elements there are Collectors.summing() methods which have the following forms for different types-
summingInt(ToIntFunction<? super T> mapper)– To get sum of stream of integers. If no elements are present, the result is 0.
summingLong ..read more
KnpCode
2y ago
If you want average of Stream elements there are handy utility methods available in Collectors class to quickly do that, the methods are-
Collectors.averagingInt()- To get average of stream of integers.
Collectors.averagingLong()- To get average of stream of longs.
Collectors.averagingDouble()- To get average of stream of doubles.
Collectors.averaging methods in Java
Syntax of these methods is as given below-
Collector<T,?,Double> averagingInt(ToIntFunction<? super T> mapper)
Collector<T,?,Double> averagingLong(ToLongFunction<? super T> mapper)
Collector<T,?,Dou ..read more