Introduction

• The Scanner class in Java is used to take user input of primitive data types like int, double, etc., and strings.
• It can read input from a user through the keyboard or from a file.
• The Scanner class is present in the java.util package.
• Syntax:

  public final class Scanner implements Iterator, Closeable
  {
      // methods
  }
  

Important Methods of Scanner Class:

• Below are some common and mostly used methods of Scanner class with examples:

Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
System.out.println(n);

Scanner sc = new Scanner(System.in);
double d = sc.nextDouble();
System.out.println(d);

Scanner sc = new Scanner(System.in);
String line = sc.nextLine();
System.out.println(line);

Scanner sc = new Scanner(System.in);
String word = sc.next();
System.out.println(word);

Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
    System.out.println(sc.next());
}

Scanner sc = new Scanner(System.in);
if(sc.hasNextInt()){
    int n = sc.nextInt();
    System.out.println(n);
}

Scanner sc = new Scanner("Java,Python,C++");
sc.useDelimiter(",");
while(sc.hasNext()){
    System.out.println(sc.next());
}

Scanner sc = new Scanner(System.in);
sc.close();

Example:

• import java.util.Scanner;
  
  public class ScannerExample
  {
      public static void main(String[] args)
      {
          Scanner sc = new Scanner(System.in);
  
          System.out.print("Enter your name : ");
          String name = sc.nextLine();
  
          System.out.print("Enter your age : ");
          int age = sc.nextInt();
  
          System.out.print("Enter your salary : ");
          double salary = sc.nextDouble();
  
          System.out.println("--------------------------------");
  
          System.out.println("Name : " + name);
          System.out.println("Age : " + age);
          System.out.println("Salary : Rs. " + salary);
  
          sc.close();
      }
  }

  Output:

  Enter your name : Deepak
  Enter your age : 30
  Enter your salary : 200000
  --------------------------------
  Name : Deepak
  Age : 30
  Salary : Rs. 200000.0

Important Points:

1. To create a Scanner object, we often pass System.in to read input from the keyboard. If we want to read from a file, we can pass a File object instead.
2. To read numbers of a particular type, use the corresponding method nextXYZ(). For example:
   • To read int values, we use nextInt() method.
   • To read short values, we use nextShort() method.
3. To read an entire line, we use nextLine() method.
   Example:

   
   import java.util.Scanner;
   
   public class MainApp
   {
       public static void main(String[] args)
       {
           Scanner sc = new Scanner(System.in);
           System.out.println("Enter a line:");
           String line = sc.nextLine();
           System.out.println("You entered: " + line);
           sc.close();
       }
   }

4. To read a single character, we use next().charAt(0).
   Example (syntax):

   
   Scanner sc = new Scanner(System.in);
   char ch = sc.next().charAt(0);
           

5. To read data from a file, we use Scanner(File file) constructor.
   Example:

   
   import java.util.Scanner;
   import java.io.File;
   import java.io.FileNotFoundException;
   
   public class ReadFile
   {
       public static void main(String[] args) throws FileNotFoundException
       {
           File file = new File("input.txt");
           Scanner sc = new Scanner(file);
           while(sc.hasNextLine())
           {
               String line = sc.nextLine();
               System.out.println(line);
           }
           sc.close();
       }
   }

6. Always close the Scanner object after use to avoid resource leaks.