#83 User Input using BufferedReader and Scanner in Java

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In this lecture we are discussing about different ways to take input in java:
how to take input from user :
in C++ we use cin
in C we use scanf()
in python we use input()

How to take input in java?
#1
using System.in.read()
— using System.in.read() we can take single character input only, if we provide multiplecharacterr
itconsidersr the firstcharacterr of enter sequence.

— if we want to show result of multiple character we can use loop (not in video lecture forcuriosityy)
e.g
class Main{
public static void main(String[] args) throws Exception{
int i =System.in.read(); // read a byte from the keyboard
System.out.println(i); // print the byte value
/*
input: a
output: 97
input: A
output: 65
input: 345 /considere 3 digit from number
output: 51
input: 3456 //consider 3 digit from number
output: 51
input: 3
output: 51

return ascii value of the input
*/
// to get actual number
// 1. convert ascii value to char
System.out.println((char)i); // print the char value

// 2. subtract 48 from the ascii value
System.out.println(i-48); // print the actual number
//but it is only for single digit number

// formultiple-digittnumbersr we have to use loop
// 3. use loop
int n=0;
while(i!=13){ // 13 is ascii value of enter key
n=n*10+(i-48);
i=System.in.read();
}
System.out.println(n);

}
}
using InputStreamReader class:
In Java, the InputStreamReader class is used to read data from an input stream and convert it into characters.
It is often used with the BufferedReader class, which provides a buffered way to read characters from an input stream.
e.g
class Main{
public static void main(String[] args) {
BufferedReader br = null;
try {
// create a new InputStreamReader to read from System.in
InputStreamReader isr = new InputStreamReader(System.in);
// create a new BufferedReader to read from the InputStreamReader
br = new BufferedReader(isr);

System.out.println(“Enter your name:”);
// read a line of text from the BufferedReader
String name = br.readLine();

System.out.println(“Hello, ” + name + “!”);
} catch (IOException e) {
System.err.println(“Error reading input: ” + e.getMessage());
}
finally{
if(br!=null){
try{
br.close();
}
catch(IOException e){
System.out.println(“There might some problem to closing the resource”);
}
}
}
}
}
Note: if open the resource then close is important

Use of Scanner Class :
To make programmer life easy
Scanner class was introduced in Java 1.5 as part of the Java API to provide an easy way
to read user input from various sources such as the keyboard.

a) Reading input through keyboard:
— import java.util.Scanner; need to import in java file

Scanner scanner = new Scanner(System.in);
System.out.print(“Enter your name: “);
String name = scanner.nextLine();
System.out.println(“Hello, ” + name + “!”);

— Scanner object using the System.in input stream, which represents the keyboard.
We then use the nextLine() method to read a line of text entered by the user.

Important: From here this part is not in video, for your cursoity we are put only in this description.

b) read through file
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

File file = new File(“input.txt”);
try {
Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
System.out.println(line);
}
} catch (FileNotFoundException e) {
System.out.println(“File not found: ” + e.getMessage());
}
we create a Scanner object using a File object that represents the input file.
We then use the hasNextLine() and nextLine() methods to read each line of text from the file.

c) Read input though String
import java.util.Scanner;

String input = “156 2 3 4 5”;
Scanner scanner = new Scanner(input);
while (scanner.hasNextInt()) {
int number = scanner.nextInt();
System.out.println(number);
}
— Scanner object using a String object that contains the input. We then use the hasNextInt() and nextInt() methods to read each integer from the string.

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