Java Programming Lesson-10 | Advanced Scanner Input & Parsing / Reading Strings & Numbers

Java Programming Lesson-10

Handling user input is one of the most important parts of programming. Whether you are building a calculator, form validation, file reader, or a real-world application, you must know how to read, parse, and process user input correctly.

In this article, you will learn Advanced Scanner Input, Parsing, and Reading Strings & Numbers in a simple way, along with useful examples.

Welcome to Lesson-10: Advanced Scanner Input & Parsing — this is essential for real-world programs where user input isn’t always simple.

✅ Scanner Class Recap

Scanner is used to take input from the user.

import java.util.Scanner;

Scanner sc = new Scanner(System.in);

Methods:

Method	Reads
nextInt()	Integer
nextFloat()	Float
nextDouble()	Double
next()	Single word String
nextLine()	Full line String

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✅ 1️⃣ Reading Numbers & Strings Together

Problem: Mixing nextInt() and nextLine() can skip input.

Scanner sc = new Scanner(System.in);
System.out.print("Enter age: ");
int age = sc.nextInt();   // reads int

sc.nextLine(); // consume leftover newline

System.out.print("Enter name: ");
String name = sc.nextLine();  // reads full line

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✅ 2️⃣ Parsing Strings to Numbers

Sometimes input comes as String, we need to convert.

String str = "123";
int num = Integer.parseInt(str);       // String → int
double d = Double.parseDouble("12.34"); // String → double

Example:

Scanner sc = new Scanner(System.in);
System.out.print("Enter a number as text: ");
String input = sc.nextLine();
int number = Integer.parseInt(input);
System.out.println("Number + 10 = " + (number + 10));

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✅ 3️⃣ Validating Input Using Try-Catch

Scanner sc = new Scanner(System.in);
System.out.print("Enter an integer: ");
try {
    int num = sc.nextInt();
    System.out.println("You entered: " + num);
} catch(Exception e) {
    System.out.println("Invalid input!");
}

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✅ 4️⃣ Reading Multiple Values in One Line

Scanner sc = new Scanner(System.in);
System.out.println("Enter 3 numbers separated by space:");
int a = sc.nextInt();
int b = sc.nextInt();
int c = sc.nextInt();

System.out.println("Sum = " + (a+b+c));

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✅ 5️⃣ Parsing Complex Input

Example: User enters "25,30,45" → split and parse

Scanner sc = new Scanner(System.in);
System.out.print("Enter numbers separated by comma: ");
String input = sc.nextLine();

String parts[] = input.split(",");
int sum = 0;

for(String p : parts){
    sum += Integer.parseInt(p.trim());
}

System.out.println("Sum = " + sum);

✅ Output (input: 10, 20, 30):

Sum = 60

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📝 Exercise for You ✅

Create a program that:

1️⃣ Takes full name as input
2️⃣ Takes age as input
3️⃣ Takes comma-separated numbers → calculates sum
4️⃣ Handles invalid number input with try-catch

Example Output:

Enter full name: Jitu Hasan
Enter age: 21
Enter numbers separated by comma: 10, 20, 30
Hello Jitu Hasan, Age: 21
Sum of numbers: 60

Reply with:
✅ Your Code
✅ Output

I’ll check & improve it 🔥

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🎯 Quick Quiz

1️⃣ Which Scanner method reads whole line?
A) next()
B) nextLine()
C) nextInt()

2️⃣ Convert "45" (String) to int?
A) Integer.parse("45")
B) Integer.parseInt("45")
C) Integer.toInt("45")

Reply like:
1 → ?, 2 → ?

Conclusion

Advanced Scanner Input and Parsing are essential skills for every programmer. They help you:

• Read clean and accurate input
• Handle strings, numbers, and mixed data
• Work with multiple values
• Avoid common errors with nextLine()
• Build real-world applications

Master this once, and you’ll find input handling in any programming language much easier.

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✅ Lesson-10 Completed!

✅ NEXT PART - Lesson-11: Object-Oriented Programming (Classes & Objects).

Frequently Asked Questions-(FAQ)

What is advanced Scanner input in Java?

Advanced Scanner input refers to techniques for reading multiple data types, handling input errors, consuming leftover newline characters, and parsing formatted values efficiently.

Why does Scanner skip input after using nextInt() or nextDouble()?

This happens because methods like nextInt() leave a newline (\n) in the buffer. To fix it, use scanner.nextLine() after reading numbers.

How can I safely parse numbers from user input in Java?

Use Integer.parseInt(), Double.parseDouble(), or wrapper classes inside try–catch blocks to prevent program crashes when users enter invalid data.

What is input validation in Java?

Input validation checks whether the user-provided data is correct (e.g., numeric, not empty, within range). It prevents errors and keeps your program safe.

How do I handle invalid user input using exception handling?

Wrap parsing code in a try–catch block. If an exception occurs, show a friendly message and prompt the user again.

How do I read full sentences using Scanner in Java?

Use nextLine() for complete sentences, including spaces. Avoid mixing it with nextInt() without clearing the buffer.

What is the difference between next(), nextLine(), and nextInt()?

next() → reads a single word nextLine() → reads the entire line nextInt() → reads an integer value Each behaves differently with the input buffer.

How can I parse Strings into numbers in Java?

int num = Integer.parseInt(str); double value = Double.parseDouble(str);

Why should I use try-catch in input parsing?

Users often give unexpected input. try-catch prevents your program from crashing and lets you show a helpful message.

How do I prevent infinite loops when validating user input?

Combine loops (like while) with exception handling. Break out of the loop only when valid input is received.