String concatenation

Learn text joining with +.

The String + operator

In Java the + operator does two things: it adds numbers and concatenates Strings. If at least one side is a String, + concatenates.

String name = "Alex";
String msg = "Hello " + name;
// "Hello Alex"

If you concatenate a String with a number, the number is automatically turned into a String:

"Age: " + 28  // "Age: 28"

Number + String

When you concatenate a String and a number with +, Java turns the number into a String and places them side by side:

int age = 28;
System.out.println("Age: " + age);
// Age: 28

Watch out: 1 + 2 + "x" first adds 1 + 2 (3), then concatenates 3 + "x" ("3x"). "x" + 1 + 2 becomes "x12" because it goes left to right.

Operator precedence and associativity matter.

Exercise Concatenate Strings

Write a Main class with a main method. Assign "Alex" to String name and 28 to int age. Print "Hello " + name + " " + age with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        String name = "Alex";
        int age = 28;
        System.out.println("Hello " + name + " " + age);
    }
}

Test yourself

Complete the concatenation

String msg = "Hello " + ____;

Show answer

String msg = "Hello " + "Alex";

Match the concatenation types

"a" + "b"

Concatenation
5 + 3

Addition
"" + 5

To string
+

Operator
Which is a String concatenation?
- 5 + 3
- 4 * 2
- 10 - 2
- "x" + 5
Show answer

"x" + 5 — String + number concatenates.

Next lesson: Math class

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