Input & Expressions – Part 2
Use nextLine safely, trim whitespace, parse numbers from text, and control concatenation vs addition with parentheses.
Input & Expressions – Part 2 is a free Java Academy lesson on CoddyKit — lesson 3 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Lesson Goals
Goals: Use nextLine() safely, trim input, parse numbers from text, and understand when + concatenates vs adds.
Newline Trap
Newline trap: After nextInt() or nextDouble(), a leftover newline may cause the next nextLine() to return empty.
Fix: call an extra nextLine() to consume it, or read lines and parse numbers.
Read Lines
Read lines with nextLine(), then trim() spaces.
String text = sc.nextLine().trim();Parse Numbers
Parse numbers from strings:
int n = Integer.parseInt("42");double x = Double.parseDouble("3.14");
Validate input in real apps to avoid crashes.
Concat vs Add
Concatenation vs addition
- If either side is a
String,+concatenates. - Use parentheses to control order:
"Total: " + (a + b). - Cast or use double literals to control numeric division.
nextLine & Concat Demo
Try it: Enter two integers as text. Notice when + concatenates and when it adds.
public class Main {
public static void main(String[] args) {
// Example input values (instead of using Scanner)
int a = 7;
int b = 3;
// Print the sum of a and b
System.out.println("a + b = " + (a + b));
// Concatenating integer a with the string "b"
System.out.println("a + \"b\" = " + (a + "b"));
// String concatenation: "2" + 3 becomes "23"
System.out.println("\"2\" + 3 = " + ("2" + 3));
// Left-to-right evaluation: (2 + 3) = 5, then "5" + "4" = "54"
System.out.println("2 + 3 + \"4\" = " + (2 + 3 + "4"));
// Adding a and b first, then concatenating with the string "Total: "
System.out.println("\"Total: \" + (a + b) = " + ("Total: " + (a + b)));
}
}
Order & Concat
Quick check: What is the output of System.out.println(2 + 3 + "4"); ?
Recap & Next
Recap: You used nextLine(), trimmed input, parsed numbers, and controlled concatenation with parentheses.
Next: Move to conditions to make decisions based on input.
Frequently asked questions
Is the “Input & Expressions – Part 2” lesson free?
Yes — the full text of “Input & Expressions – Part 2” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “Input & Expressions – Part 2”?
Use nextLine safely, trim whitespace, parse numbers from text, and control concatenation vs addition with parentheses. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Input & Expressions – Part 2” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Variables & Data Types
- Input & Expressions – Part 1
- Input & Expressions – Part 2