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. This is 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, and your progress syncs across the web and the CoddyKit app. The Java Academy course includes 3 lessons in total.
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.
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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. 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. The Java Academy course includes 3 lessons in total.
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, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 3.
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