new Scanner() / scanner.nextLine() / nextInt()

// Creates a Scanner that reads from standard input (keyboard).
Scanner scanner = new Scanner(System.in);

// Reads an entire line as a String.
String line = scanner.nextLine();

// Reads the next token (delimited by whitespace) as a String.
String word = scanner.next();

// Reads an integer.
int num = scanner.nextInt();

// Reads a double.
double d = scanner.nextDouble();

// Checks whether there is another line to read.
scanner.hasNextLine();

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);

// Reads one line for the name.
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name + "!");

// Reads an integer.
System.out.print("Enter your age: ");
int age = scanner.nextInt();
System.out.println("Next year you will be " + (age + 1) + ".");

// After calling nextInt(), consume the leftover newline before calling nextLine().
scanner.nextLine(); // Discards the newline remaining in the buffer.

// Reads multiple lines.
System.out.println("Enter text (type 'end' to finish):");
while (scanner.hasNextLine()) {
    String line = scanner.nextLine();
    if (line.equals("end")) break;
    System.out.println("Input: " + line);
}

// Close the scanner when done.
scanner.close();

When you call nextLine() immediately after a method like nextInt(), it reads the leftover newline character in the buffer and returns an empty string. To avoid this, call scanner.nextLine() once right after reading a number to consume that newline.

If the input cannot be parsed as the expected type, an InputMismatchException is thrown. To handle user input safely, either use a try-catch block or read the input with nextLine() and convert it manually using Integer.parseInt().

For buffered input reading, see new BufferedReader() / readLine().