String Concatenation

We already have +, -, *, /, and %. But + has a second talent: besides adding numbers, it can glue text together. This is the classic Java way to combine text and variables

public class Main {
    public static void main(String[] args) {
        String name = "Quincy";
        int age = 32;
        double height = 1.97;

        System.out.println("Hello. My name is " + name + ", I am " + age + " years old and " + height + " m tall");
    }
}

Output

Hello. My name is Quincy, I am 32 years old and 1.97 m tall

What is happening here? When we put a String and another value together with +, Java converts everything to text and glues them. This is called string concatenation

Watch the spaces carefully

"Hello. My name is " + name

We have a space before the closing quote, otherwise we’d get Hello. My name isQuincy all stuck together. This is something almost everyone gets wrong at first. Always check your spaces

A small but very important subtlety

public class Main {
    public static void main(String[] args) {
        System.out.println("Result: " + 2 + 3);
    }
}

What do you think this prints? Result: 5?

It prints Result: 23

Why? Java reads from left to right. It starts with "Result: " (a String), then sees + 2: a String + an int = String, so it becomes "Result: 2". Then + 3 → "Result: 23"

If we want 5, we use parentheses to force the math first

public class Main {
    public static void main(String[] args) {
        System.out.println("Result: " + (2 + 3));
    }
}

Output

Result: 5

Now (2 + 3) is computed first (giving 5), then glued to the string. Remember this rule, you will hit it in real code

+ is enough for simple cases, but when you have a lot of text to combine it gets hard to read, full of quotes and + signs. Java has a cleaner alternative: String.format()

public class Main {
    public static void main(String[] args) {
        String name = "Tommy Vercetti";
        String message = String.format("Hello, %s!", name);
        System.out.println(message);
    }
}

Output

Hello, Tommy Vercetti!

%s is a placeholder: it means "put a String here". When Java runs String.format(...), it replaces %s with the value of name. Think of it as a template where you fill in the blanks

There are different placeholders for different types

• %s: String (or anything else, Java converts it to text)
• %d: whole number (int)
• %f: number with a decimal point (double)

public class Main {
    public static void main(String[] args) {
        String player = "Lance Vance";
        int kills = 47;
        double accuracy = 82.5;

        System.out.println(String.format("Player: %s | Kills: %d | Accuracy: %f", player, kills, accuracy));
    }
}

Output

Player: Lance Vance | Kills: 47 | Accuracy: 82.500000

Wait, that’s a lot of decimals! By default, %f prints 6 decimals. To control that, use %.Nf, where N is the number of decimals you want

%.2f means "print 2 decimals". This is the one you’ll use most often

public class Main {
    public static void main(String[] args) {
        double price = 4.5;
        System.out.println(String.format("Price: $%.2f", price));
    }
}

Output

Price: $4.50

Java also has printf(), which formats AND prints in a single step, so you don’t need a separate String.format() plus System.out.println()

public class Main {
    public static void main(String[] args) {
        String name = "Tommy";
        int score = 1500;
        System.out.printf("Player: %s | Score: %d%n", name, score);
    }
}

Notice the %n at the end: that is the newline character for printf. Without it, the next print would continue on the same line

Use whichever you prefer. String.format() is great when you want to store the text in a variable, and printf() is great when you just want to print it right away

Mission: Scoreboard

The station’s arcade just finished a tournament. Print the winner’s stats on a single line.

Create three variables: name (String) for the player’s name, score (int) for the total score, and rating (double) for the performance rating. Then print a line of the form Player: <name> | Score: <score> | Rating: <rating>. You can use + or String.format(), whichever you prefer.

Example

With the name Tommy Vercetti, the score 1500, and the rating 4.75, your program should print

Player: Tommy Vercetti | Score: 1500 | Rating: 4.75