Java How to Convert Double to Int - Simple Examples

In Java, convert a double to an int by using explicit casting like int result = (int) yourDouble; which truncates the decimal part.

Examples

Input12.99

Output12

Input45.0

Output45

Input-3.7

Output-3

How to Think About It

To convert a double to an int, think about removing the decimal part because int only holds whole numbers. You do this by telling Java to treat the double as an int using casting, which cuts off anything after the decimal point without rounding.

Algorithm

1

Take the double value as input.

2

Use explicit casting to convert the double to int.

3

Store or use the resulting int value.

Code

java

public class ConvertDoubleToInt {
    public static void main(String[] args) {
        double myDouble = 9.78;
        int myInt = (int) myDouble; // cast double to int
        System.out.println(myInt); // prints 9
    }
}

Output

9

Dry Run

Let's trace converting 9.78 to int through the code

1

Start with double value

myDouble = 9.78

2

Cast double to int

myInt = (int) 9.78 results in 9

3

Print int value

Output is 9

Step	Value of myDouble	Value of myInt	Output
1	9.78	N/A	N/A
2	9.78	9	N/A
3	9.78	9	9

Why This Works

Step 1: Casting removes decimals

Using (int) tells Java to convert the double to an int by dropping the decimal part.

Step 2: No rounding happens

Casting truncates the number, so 9.78 becomes 9, not 10.

Step 3: Result is stored as int

The result is stored in an int variable which can only hold whole numbers.

Alternative Approaches

Using Math.round() before casting

java

public class ConvertDoubleToInt {
    public static void main(String[] args) {
        double myDouble = 9.78;
        int myInt = (int) Math.round(myDouble); // rounds before casting
        System.out.println(myInt); // prints 10
    }
}

This rounds the double to the nearest whole number before converting, unlike simple casting which truncates.

Using Double.intValue() method

java

public class ConvertDoubleToInt {
    public static void main(String[] args) {
        Double myDouble = 9.78;
        int myInt = myDouble.intValue(); // converts to int by truncation
        System.out.println(myInt); // prints 9
    }
}

This uses the Double wrapper class method but also truncates decimals.

Complexity: O(1) time, O(1) space

Time Complexity

Casting a double to int is a simple operation done in constant time without loops.

Space Complexity

No extra memory is needed beyond the variables used, so space is constant.

Which Approach is Fastest?

Simple casting is fastest and most direct; using Math.round() adds a small overhead for rounding.

Approach	Time	Space	Best For
Explicit casting (int)	O(1)	O(1)	Fast truncation without rounding
Math.round() then cast	O(1)	O(1)	When rounding is needed
Double.intValue() method	O(1)	O(1)	Using wrapper class, truncates decimals