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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.

Practice 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.

Sample solution

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

Expected output

Hello Alex 28

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Complete the concatenation

Question 
String msg = "Hello " + ____;
Answer 
String msg = "Hello " + "Alex";

Explanation: Two Strings are joined with +.

2 Match the concatenation types

Term Meaning
"a" + "b" Concatenation
5 + 3 Addition
"" + 5 To string
+ Operator

3 Which is a String concatenation?

  • 5 + 3
  • 4 * 2
  • 10 - 2
  • "x" + 5 Correct answer

Explanation: String + number concatenates.

All lessons in Beginner

1 Java basics

  1. What is Java?
  2. The main method
  3. Comments
  4. Class skeleton
  5. javac and java
  6. Summary - Java basics

2 Variables

  1. int and double
  2. boolean
  3. String
  4. Naming variables
  5. final variables
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Type casting
  3. String concatenation
  4. Math class
  5. BigInteger and BigDecimal
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Assignment and increment
  6. Summary - Operators

6 String basics

  1. length and charAt
  2. equals and equalsIgnoreCase
  3. indexOf and substring
  4. toUpperCase and trim
  5. String.format
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and else if
  3. Nested if
  4. switch
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. do-while
  4. break and continue
  5. for-each
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Filling arrays
  4. Multi-dimensional arrays
  5. Copying arrays
  6. Summary - Arrays

11 Array methods

  1. Arrays.sort
  2. Arrays.toString
  3. Arrays.binarySearch
  4. Arrays.copyOf
  5. Arrays.fill
  6. Summary - Array methods

12 Collections

  1. ArrayList
  2. add and get
  3. HashMap
  4. put and get
  5. HashSet
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. return
  3. void methods
  4. Method overloading
  5. Scope
  6. Summary - Methods

14 Method parameters

  1. Primitive parameters
  2. Object parameters
  3. varargs
  4. Multiple values via array
  5. final parameters
  6. Summary - Method parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String builder

  1. StringBuilder
  2. append
  3. insert and delete
  4. reverse
  5. toString
  6. Summary - String builder

17 Input and output

  1. Scanner
  2. nextInt and nextLine
  3. System.out.printf
  4. BufferedReader
  5. try-with-resources
  6. Summary - Input and output

18 Enum

  1. Declaring enums
  2. values and valueOf
  3. Enum fields
  4. Enum methods
  5. switch with enum
  6. Summary - Enum

19 Exception basics

  1. try/catch
  2. finally
  3. throw
  4. Exception hierarchy
  5. Multiple catch
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together