Input and Output in Java

🧠 Topic: Input and Output in Java

💻 What is Input and Output?

Input → This is how a program receives data.
Output → This is how a program shows or returns data.

Think of it like this:

Input = You talking to the computer (e.g., typing or clicking).
Output = Computer talking back to you (e.g., showing results on screen).

Example:

When you type something in a form → that’s input.
When the program displays your result → that’s output.

🖨 OUTPUT in Java

Output is basically the program’s response — the result shown after processing something.

In Java, we use:

System.out.println("Hello World!");

Let’s break that down 👇

Part	Meaning
`System`	A built-in Java class that handles system-level stuff (like input/output).
`out`	Refers to the standard output device (usually your screen).
`println()`	A method that prints text and then moves the cursor to the next line.

So, this line:

System.out.println("Hello World!");

➡ Displays Hello World! and moves the cursor to the next line.

If you remove the “ln”, like this:

System.out.print("Hello World!");

➡ It’ll still print Hello World!, but the cursor stays on the same line.

✨ Examples of Output Methods

Code	Output	Explanation
`System.out.println("Hello");` `System.out.println("World!");`	Hello World!	Each `println` moves to a new line
`System.out.print("Hello");` `System.out.print("World!");`	HelloWorld!	Stays on one line (no space)
`System.out.print("Hello ");` `System.out.print("World!");` `System.out.println();`	Hello World!	Adds space + moves to next line

Pro Tip 💡:
System.out.println(); by itself makes a blank line — but only if there’s no print before it.

⌨ INPUT in Java

Now let’s talk about getting input from the user (like typing something in the console).

Java doesn’t support input directly — we need a Scanner to do that.

You start with:

import java.util.Scanner;

This line imports the Scanner class, which allows the program to read input from the keyboard.

🧩 Sample Input Program

import java.util.*;  

class InputOutput {
    public static void main(String[] args) {
        int num;
        Scanner scanner;
        scanner = new Scanner(System.in);
        
        System.out.print("Enter an integer: "); // prompt
        num = scanner.nextInt();
        
        System.out.println("The integer is " + num);
    }
}

🕵‍♀️ Step-by-Step Explanation

import java.util.*;
- This gives access to the Scanner class (and other useful ones).
- The * means “import everything” in that package.
Scanner scanner = new Scanner(System.in);
- Creates a Scanner object named scanner.
- System.in = standard input device (keyboard).
System.out.print("Enter an integer: ");
- Displays a prompt (so the user knows what to type).
num = scanner.nextInt();
- Reads the integer typed by the user and stores it in the variable num.
System.out.println("The integer is " + num);
- Shows the output (the number entered).

Output Example:

Enter an integer: 8
The integer is 8

🔍 Other Useful Scanner Methods

Method	What it Reads	Example
`nextInt()`	Integer (whole number)	8
`nextDouble()`	Decimal number	3.14
`next()`	Single word	"Hello"
`nextLine()`	Whole line of text	"Hello World"

⚖ Quick Comparison: Input vs Output

Feature	Input	Output
Purpose	To get data from user	To show data to user
Device Used	Keyboard, mouse, etc.	Monitor, printer, etc.
Java Keyword	`System.in`	`System.out`
Common Method	`nextInt()`, `nextLine()`	`print()`, `println()`

🧩 Summary / In Short:

Input = what the computer receives.
Output = what the computer shows back.
Scanner → for input.
System.out.print / println → for output.
ln means “move to the next line.”

💡 Memory Trick (Para di mo makalimutan!)

🧠 Think of I/O as “In & Out” — like breathing!

You inhale = Input (get data)
You exhale = Output (show data)

Or use this mnemonic:

“I Scan In, I Print Out.”
(Scanner for Input, Print for Output 😉)