Type casting

Learn type casting with (int), (double).

What is type casting?

Converting one type to another is called type casting. Java has two kinds: widening (automatic) and narrowing (explicit cast).

Widening happens automatically from a smaller to a larger type: int → long → double. No data is lost.

Narrowing needs an explicit cast like (int) from a larger to a smaller type. Data may be lost:

double d = 3.7;
int i = (int) d;  // i = 3

The fractional part is lost.

Exercise Cast int and double

Write a Main class with a main method. Assign 9.99 to double price. Assign (int) price to int whole. Print whole with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        double price = 9.99;
        int whole = (int) price;
        System.out.println(whole);
    }
}

When do you need a cast?

A cast is needed when you convert a larger type to a smaller one. For example, to store a double result as an int you use (int).

Widening conversion is automatic: no cast is needed to turn an int into a double. The compiler does it for you.

Before casting, consider whether data may be lost. For example, going from long to int may overflow if the value exceeds the int range.

Test yourself

Match the casting types

Widening

Automatic
Narrowing

Explicit cast
(int)

Cast operator
double→int

Data loss
What happens when you cast double 3.7 to int?
- Stays 3.7
- Becomes 4, rounded
- Becomes 3, fraction lost
- Throws an error
Show answer

Becomes 3, fraction lost — Narrowing cast drops the fraction, leaving 3.
Complete the cast operator
```
int x = ____ 3.7;
```
Show answer
```
int x = (int) 3.7;
```

Next lesson: String concatenation

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