Java — Output

System.out.println

The most basic output command in Java:

System.out.println("Hello, world!");

println prints the text and moves to the next line. Think of it as "print line."

System.out.print vs System.out.println

System.out.print("Hello ");
System.out.print("world!");
System.out.println();
System.out.println("Done.");

Output:

Hello world!
Done.

print stays on the same line. println adds a newline after printing. Use print when you want to build output piece by piece.

Printing numbers and expressions

System.out.println(42);
System.out.println(3.14);
System.out.println(2 + 3);
System.out.println("Result: " + (2 + 3));

Output:

42
3.14
5
Result: 5

Notice the difference: 2 + 3 without quotes does math. "Result: " + (2 + 3) concatenates a string with the result. Parentheses force the math to happen first.

Concatenation

The + operator joins strings together:

String greeting = "Hello";
String name = "Ada";
System.out.println(greeting + ", " + name + "!");

Output:

Hello, Ada!

Every value can be converted to a string automatically when joined with one. Java calls this string conversion — numbers, booleans, even objects become their text representation.

printf — formatted output

For precise control over formatting, use printf:

String name = "Ada";
int age = 36;
double gpa = 3.85;

System.out.printf("Name: %s%n", name);
System.out.printf("Age: %d%n", age);
System.out.printf("GPA: %.2f%n", gpa);

Output:

Name: Ada
Age: 36
GPA: 3.85

Common format specifiers:

Specifier	Meaning	Example
%s	String	"Ada"
%d	Integer	42
%f	Float/double	3.85
%.2f	Float with 2 decimals	3.85
%n	Platform-independent newline	\n on most systems

printf shines when you need aligned columns or precise decimal places — things println can't do cleanly.

Reading user input with Scanner

Java doesn't have a built-in input() function like Python. Instead, you use the Scanner class:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("What is your name? ");
        String name = sc.nextLine();

        System.out.print("How old are you? ");
        int age = sc.nextInt();

        System.out.printf("Hello %s, you are %d years old.%n", name, age);
        sc.close();
    }
}

Output:

What is your name? Ada
How old are you? 36
Hello Ada, you are 36 years old.

Three things to note:

• nextLine() reads an entire line of text
• nextInt() reads a single integer — if the user types text, it crashes
• Always close() the scanner when done to free system resources

Scanner methods overview

Method	Reads
nextLine()	Entire line of text
next()	Single word (stops at whitespace)
nextInt()	An integer
nextDouble()	A decimal number
nextBoolean()	A boolean value

The method you choose must match what the user types. Typing "hello" when nextInt() expects a number throws an InputMismatchException. Validate or catch it.

println with multiple values

int x = 5;
int y = 10;
System.out.println("x = " + x + ", y = " + y);

Output:

x = 5, y = 10

Java concatenates everything into one string before printing. There's no limit to how many values you chain together.

Escaping special characters

Some characters can't be typed directly inside a string:

System.out.println("She said \"hello\"");
System.out.println("Line one\nLine two");
System.out.println("Path: C:\\Users\\Ada");

Output:

She said "hello"
Line one
Line two
Path: C:\Users\Ada

Escape	Represents
\"	Double quote
\n	Newline
\t	Tab
\\	Backslash

Mini Practice

1. Print a receipt: item name, quantity, and price on separate lines
2. Use printf to print a number with exactly 3 decimal places
3. Ask the user for their name and birth year — calculate and print their age
4. Print a multi-line poem using \n escape sequences
5. Try using nextInt() then nextLine() — observe the newline bug and fix it with an extra nextLine() call

Next: commenting your code effectively →