Strings & Messages

A String is text, including spaces and punctuation. Double quotes mark its boundaries in source code; they are not printed as part of its value. You can store text in a variable and reuse it in several messages. An empty string, written as two adjacent double quotes, is valid text of length zero.

The + operator adds numbers when both operands are numeric. If a String is involved, it builds text instead. Java evaluates a chain from left to right, so adding a label before two numbers can turn those later operations into text concatenation. Use parentheses or a named numeric result to make your intention clear. A readable report is the last step of a calculation, not a replacement for the calculation.

Let names carry meaning

Build messages from values rather than repeatedly editing the same number in several strings. If minutes changes from 25 to 30, every message using that variable sees its current value. You still decide where the spaces go. Java does not automatically insert spaces between concatenated pieces.

public class Main {
    public static void main(String[] args) {
        String topic = "Java";
        int minutes = 25;
        int sessions = 2;
        int total = minutes * sessions;

        System.out.println(topic + ": " + total + " min");
        System.out.println("Next: " + topic);
    }
}

Java: 50 min
Next: Java

The total is a number until the print statement combines it with a label. The colon and spaces belong to quoted text. Change minutes to 30 and confirm that the report follows the value.

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

Total: 23
Total: 5
5 minutes

The first line builds Total: 2, then appends 3. The parentheses in the second line require numeric addition first. The last line starts with two numbers, so it adds them before encountering text.

public class Main {
    public static void main(String[] args) {
        String title = "Java";
        String spaced = " Java ";

        System.out.println(title.length());
        System.out.println(spaced.length());
        System.out.println("".length());
    }
}

4
6
0

length() is a built-in String method: a named operation that gives back a value. Include its parentheses. The two outer spaces are real characters. Later you will learn more String operations and write methods of your own.

Your turn

public class Main {
    public static void main(String[] args) {
        String topic = "Loops";
        int days = 3;
        int minutesPerDay = 20;
        // Calculate the total and build the report.
    }
}

public class Main {
    public static void main(String[] args) {
        String topic = "Loops";
        int days = 3;
        int minutesPerDay = 20;
        int total = days * minutesPerDay;

        System.out.println(topic + ": " + total + " minutes in " + days + " days");
        System.out.println(topic.length());
    }
}

Loops: 60 minutes in 3 days
5

Change it and explain

Use a topic with an internal space and predict its length. Try days=1; the message still says days because grammar is not automatic. You will learn how to choose singular or plural wording using conditions tomorrow.

To put a double quote inside text, escape it as \"; a backslash introduces an escape sequence in a Java string. \n represents a newline in text, while a newline between statements only changes source layout. Prefer separate println calls while practising output order. Do not use String equality with == to compare user-facing text; the dedicated equality lesson will explain why.

Going further

These examples use simple English text. Java’s length() counts UTF-16 code units, so a visible symbol such as an emoji can count as two rather than one. charAt uses the same positions. You do not need Unicode processing for this course’s core tasks; avoid assuming that a displayed symbol always occupies one position.