Module 3: Operators, Expressions, and Strings

String Basics and Concatenation

Store text in strings and combine text with values to make output more useful.

Author

Java Learner Editorial Team

Reviewer

Technical review by Java Learner

Last reviewed

2026-04-16

Java version

Java 25 LTS

How this lesson was prepared: AI-assisted draft, edited by hand, and checked against current Java 25 documentation and runnable examples.

Learning goals

Declare and print strings
Concatenate strings with `+`
Mix text with variables in readable output

What a string is: A String stores text such as names, messages, and labels. Strings use double quotes.

Concatenation: The + operator also joins strings together. This is called concatenation.

Mixing text and values: You can combine strings with numbers and booleans to build friendly output messages.

Why this matters: Most programs need readable output, prompts, labels, and messages, not just raw numbers.

Runnable examples

Join two pieces of text

public class Main {
    public static void main(String[] args) {
        String first = "Java";
        String second = "Learner";
        System.out.println(first + " " + second);
    }
}

Expected output

Java Learner

Combine text with a variable

public class Main {
    public static void main(String[] args) {
        int lessons = 4;
        System.out.println("Completed lessons: " + lessons);
    }
}

Expected output

Completed lessons: 4

Common mistakes

Using single quotes for multi-character text

Strings use double quotes, like `"Hello"`.

Mini exercise

Create a string for your name and print `Hello, <name>`.

Summary

Strings store text.
The `+` operator can join strings together.

Next step

Once strings feel comfortable, use a few helpful string methods.

Sources used

String Basics and Concatenation

Join two pieces of text

Combine text with a variable

Which line creates a valid string variable?