Java Scanner & Interactive Input
The `Scanner` class from the `java.util` package is the standard tool for reading user input in console applications. It parses primitive types and strings using regular expressions from `System.in`.
"Scanner is like an attentive stenographer listening to System.in. When you ask for an integer with .nextInt(), it listens until a number is typed and delivers it into your variable."
Deep Dive: How It Works
Import required: `import java.util.Scanner;` at the top of your file.
Instantiation: `Scanner scanner = new Scanner(System.in);`
Methods: `.nextLine()` (reads full line text), `.next()` (reads single word), `.nextInt()`, `.nextDouble()`, `.nextBoolean()`.
Closing: Call `scanner.close()` when finished to release system resources.
Syntax Blueprint
import java.util.Scanner; Scanner sc = new Scanner(System.in); String name = sc.nextLine(); int age = sc.nextInt(); sc.close();
Always import Scanner from java.util and instantiate with System.in.
Core Rules to Remember
Common Beginner Traps & How to Fix Them
Calling nextLine() immediately after nextInt()Why it happens: nextInt() consumes the number but leaves the newline character in the buffer.
How to fix: Call an extra scanner.nextLine() to consume the leftover newline before reading text.
Live Interactive Example
Hit Run Code to see it liveYour Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Read and double an input number
- Read the integer from the scanner.
- Multiply it by 2 and print "Double: " + (num * 2).
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