Reading string input in Java - Step-by-Step Execution

Concept Flow - Reading string input

Start Program

↓

Create Scanner

↓

Prompt User

↓

Wait for Input

↓

Read Input String

↓

Store in Variable

↓

Use or Print String

↓

End Program

The program starts, creates a Scanner to read input, waits for the user to type a string, stores it, then uses or prints it.

Execution Sample

Java

import java.util.Scanner;

public class Main {
    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 the full line as a string, then greets the user.

Execution Table

Step	Action	Input/Condition	Variable State	Output
1	Create Scanner object	N/A	sc = Scanner(System.in)
2	Print prompt	N/A	sc = Scanner(System.in)	Enter your name:
3	Wait for user input	User types: Alice	sc = Scanner(System.in)
4	Read input line	sc.nextLine()	name = "Alice"
5	Print greeting	N/A	name = "Alice"	Hello, Alice!
6	Program ends	N/A	name = "Alice"

💡 Program ends after printing greeting.

Variable Tracker

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

Key Moments - 2 Insights

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

sc.nextLine() reads the entire line including spaces, while sc.next() reads only up to the first space. See execution_table step 4 where the full input "Alice" is read.

What happens if the user just presses Enter without typing anything?

sc.nextLine() reads an empty string "" and stores it in name. The program still continues normally as shown in execution_table step 4.

Visual Quiz - 3 Questions

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

A "Alice"

B null

C "Enter your name:"

D Scanner(System.in)

💡 Hint

Check the 'Variable State' column at step 4 in the execution_table.

At which step does the program print the greeting message?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Output' column in the execution_table to find when greeting is printed.

If the user input was "Bob Smith", which method ensures the full name is read?

A sc.next()

B sc.nextLine()

C System.out.print()

D Scanner(System.in)

💡 Hint

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

Concept Snapshot

Reading string input in Java:
- Create Scanner: Scanner sc = new Scanner(System.in);
- Prompt user: System.out.print("Enter: ");
- Read full line: String s = sc.nextLine();
- Use the string as needed
- nextLine() reads entire line including spaces
- Always close Scanner when done (not shown here)

Full Transcript

This example shows how Java reads string input from the user. First, a Scanner object is created to read from the keyboard. Then the program prints a prompt asking the user to enter their name. It waits for the user to type and press Enter. The method nextLine() reads the entire line typed, including spaces, and stores it in the variable 'name'. Finally, the program prints a greeting using the entered name. The execution table traces each step, showing variable changes and output. Key points include why nextLine() is used instead of next(), and what happens if the user inputs an empty line.