1. What is this?
A variable is a named slot holding a value. A type is the kind of value allowed: int (whole numbers), double (decimals), String (text), boolean (true/false). Java requires you to declare the type: int age = 28 means 'slot age holds whole numbers, starting at 28'.
2. Why do we use it?
Types catch whole categories of bugs before the program runs — you cannot accidentally store text in an age.
3. Syntax breakdown
int age = 28;
Declares an int variable age with value 28.
String name = "Ava";
String holds text. Note the capital S.
System.out.println(name + " is " + age);
+ joins (concatenates) strings and values into one line.
5. Common mistakes
- int age = "28" — quotes make it text, which does not fit an int.
- Using = when comparing (use == for comparison).
- Forgetting that String needs double quotes, char needs single quotes.
Practice task
Add String city = "Berlin"; and print "I live in Berlin." using + joining.
Hint
Declare the variable, then println("I live in " + city + ".");
Try it below — tests run automatically when you press Run.
Output
Press Run to see output.
Mini quiz
3 questions. Answer, then check.
1. Which type holds whole numbers?
2. Which holds text?
3. What does + do between strings?