How to Convert double to long in Java?

In this tutorial, you will learn how to convert a double value to a long in Java. We’ll explore explicit casting, handle potential precision loss, and demonstrate examples of rounding techniques for accurate results.

Java – Convert double to long

Converting double to long in Java – In Java, converting a double to a long requires explicit casting because double is a floating-point type, while long is an integer type. This conversion will truncate the decimal portion of the double value, keeping only the whole number part.

Explicit Conversion from double to long

To convert a double to a long in Java, you need to use an explicit cast. This tells the compiler to truncate the decimal part and only keep the integer portion.

Example of Explicit Conversion

public class DoubleToLongExample {

    public static void main(String[] args) {
        double doubleVal = 9.99;
        long longVal = (long) doubleVal; // Explicit conversion from double to long
        System.out.println("Double value: " + doubleVal);
        System.out.println("Long value after conversion: " + longVal);
    }
}

Output

Double value: 9.99
Long value after conversion: 9

In this example, the double value 9.99 is converted to a long, resulting in 9 as the decimal portion is truncated.

Rounding Before Conversion

If you want to round the double value to the nearest whole number before converting it to long, you can use Math.round(). This method rounds the double value to the nearest whole number and returns a long.

Example of Rounding Before Conversion

public class DoubleToLongExample {

    public static void main(String[] args) {
        double doubleVal = 9.99;
        long longVal = Math.round(doubleVal); // Rounding and converting to long
        System.out.println("Double value: " + doubleVal);
        System.out.println("Long value after rounding: " + longVal);
    }
}

Output

Double value: 9.99
Long value after rounding: 10

In this example, Math.round() rounds 9.99 up to 10 before converting it to a long.

Conclusion

Converting a double to a long in Java requires explicit casting, which truncates the decimal part. If you need to round the value, Math.round() can provide the nearest whole number before conversion. Be cautious of potential precision loss due to truncation.