ScannerInput.java

package Phase0_SetupAndFirstPrograms.Input;

import java.util.Scanner;

/**
 * <h1>Taking Input &mdash; java.util.Scanner</h1>
 *
 * <p>Scanner (since Java 5) is the easiest way to read input from the user.
 * It wraps an InputStream (<code>System.in</code> for the console, but it can also
 * read from files, strings, etc.) and provides typed convenience methods like
 * <code>nextInt()</code>, <code>nextDouble()</code>, <code>nextLine()</code>.</p>
 *
 * <h2>Typical Methods</h2>
 * <pre>
 * nextByte() - reads next token as byte
 * nextShort() - reads next token as short
 * nextInt() - reads next token as int
 * nextLong() - reads next token as long
 * nextFloat() - reads next token as float
 * nextDouble() - reads next token as double
 * nextBoolean() - reads next token as boolean
 * next() - reads next WORD (whitespace-delimited)
 * nextLine() - reads the rest of the CURRENT LINE (including spaces)
 * </pre>
 *
 * <h2>The classic "Scanner Pitfall"</h2>
 * <p>After calling <code>nextInt()</code> / <code>nextDouble()</code> etc., a newline
 * character ('\n') is left in the buffer. A subsequent <code>nextLine()</code> will
 * read that empty line instead of waiting for new input. The fix is to call an extra
 * <code>sc.nextLine()</code> to consume the leftover newline. The example below
 * demonstrates both the bug and the fix.</p>
 *
 * <h2>Closing the Scanner</h2>
 * <p>Scanner implements Closeable. Closing the Scanner that wraps <code>System.in</code>
 * also closes <code>System.in</code> for the rest of the JVM &mdash; so be careful. For
 * console apps it is fine, but if multiple parts of your program read input, leave it
 * open.</p>
 *
 * @author Deepak Gupta
 * @version 1.0
 * @since 2026-05-21
 */

public class ScannerInput {

 public static void main(String[] args) {
 Scanner sc = new Scanner(System.in);

 // 1) Read an int
 System.out.print("Enter your age : ");
 int age = sc.nextInt();

 // 2) Read a double
 System.out.print("Enter your height: ");
 double height = sc.nextDouble();

 // 3) IMPORTANT - consume the leftover newline before calling nextLine()
 sc.nextLine();

 // 4) Read a full line (with spaces)
 System.out.print("Enter your name : ");
 String name = sc.nextLine();

 System.out.println();
 System.out.println("Hello " + name + "!");
 System.out.println("You are " + age + " years old and " + height + "m tall.");

 sc.close();

 // SAMPLE RUN
 // Enter your age : 25
 // Enter your height: 1.78
 // Enter your name : Deepak Gupta
 //
 // Hello Deepak Gupta!
 // You are 25 years old and 1.78m tall.
 }
}