Using Scanner class in Java - Step-by-Step Execution

Concept Flow - Using Scanner class

Start Program

↓

Create Scanner object

↓

Prompt user for input

↓

Wait for user input

↓

Read input using Scanner

↓

Store input in variable

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Use input in program

↓

Close Scanner

↓

End Program

The program creates a Scanner to read user input, waits for input, stores it, uses it, then closes the Scanner.

Execution Sample

Java

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter your name: ");
        String name = sc.nextLine();
        System.out.println("Hello, " + name + "!");
        sc.close();
    }
}

This code asks the user to enter their name, reads it using Scanner, then greets the user.

Execution Table

Step	Action	Evaluation	Result
1	Create Scanner object sc	sc = new Scanner(System.in)	Scanner ready to read input
2	Print prompt	System.out.print	Displays: Enter your name:
3	Wait for user input	User types 'Alice' and presses Enter	Input buffer has 'Alice'
4	Read input with sc.nextLine()	Reads 'Alice'	name = 'Alice'
5	Print greeting	System.out.println("Hello, " + name + "!")	Displays: Hello, Alice!
6	Close Scanner	sc.close()	Scanner closed
7	Program ends	No more code	Program terminates

💡 Program ends after greeting and closing Scanner

Variable Tracker

Variable	Start	After Step 4	Final
sc	null	Scanner(System.in)	closed Scanner
name	null	"Alice"	"Alice"

Key Moments - 3 Insights

Why do we need to close the Scanner?

Closing the Scanner frees system resources. See step 6 in execution_table where sc.close() is called.

What happens if the user types nothing and presses Enter?

sc.nextLine() reads an empty string "" and stores it in name. This is shown in step 4 where input is read.

Why do we use nextLine() instead of next()?

nextLine() reads the whole line including spaces, while next() reads only until the first space. This ensures full input is captured as in step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'name' after step 4?

A "Hello"

B "Alice"

C null

D Scanner object

💡 Hint

Check the 'Result' column in row for step 4 in execution_table.

At which step is the Scanner closed?

A Step 2

B Step 3

C Step 6

D Step 7

💡 Hint

Look for the action 'Close Scanner' in execution_table.

If the user inputs 'Bob Smith', which method ensures the full name is read?

A sc.nextLine()

B sc.next()

C sc.nextInt()

D sc.close()

💡 Hint

Refer to key_moments about difference between next() and nextLine().

Concept Snapshot

Using Scanner class in Java:
- Import java.util.Scanner
- Create Scanner with System.in
- Use methods like nextLine() to read input
- Store input in variables
- Close Scanner after use
- Scanner reads user input from keyboard

Full Transcript

This example shows how to use the Scanner class in Java to read user input. First, we create a Scanner object connected to System.in, which is the keyboard input. Then, we prompt the user to enter their name. The program waits until the user types something and presses Enter. Using sc.nextLine(), the program reads the entire line of input and stores it in the variable 'name'. Next, it prints a greeting using the input. Finally, the Scanner is closed to free resources, and the program ends.