Java Math.round() - Examples

Java Math round

round() returns closest long to the argument passed.

Following is the syntax of round() method.

double rounded = round(double x)

Since the definition of round() function has double datatype as argument, you can also pass floating point value as argument; because float could implicitly promote to double.

We shall learn about some of the special cases for round() method with examples.

Example 1 Mathrounddouble

In the following example, we use round() method to round the given double number.

Java Program

public class MathExample {
	public static void main(String[] args) {
		double a = 20.4;
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

If the input double value has a decimal part of exactly 0.5, then round() method rounds the argument towards the positive infinity.

Java Program

public class MathExample {
	public static void main(String[] args) {
		double a = 20.5;
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

Example 2 Mathroundfloat

In the following example, we pass an float value as argument to round() method.

Java Program

public class MathExample {
	public static void main(String[] args) {
		float a = 2.1255F;
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

Example 3 MathroundNaN

In the following example, we pass Double.NaN as argument to round() method. As per the definition of the round() in Math class, the method should return zero.

Java Program

public class MathExample {
	public static void main(String[] args) {
		double a = Double.NaN; 
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

Example 4 Mathround With Positive Infinity as Argument

In the following example, we pass Double.POSITIVE_INFINITY as argument to round() method. As per the definition of the round() method in Math class, the method should return Long.MAX_VALUE.

Java Program

public class MathExample {
	public static void main(String[] args) {
		double a = Double.POSITIVE_INFINITY; 
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

9223372036854775807

Example 5 Mathround With Negative Infinity as Argument

In the following example, we pass Double.POSITIVE_INFINITY as argument to round() method. As per the definition of the round() method in Math class, the method should return Long.MIN_VALUE.

Java Program

public class MathExample {
	public static void main(String[] args) {
		double a = Double.NEGATIVE_INFINITY; 
		long rounded = Math.round(a);
		System.out.println(rounded);
	}
}

Output

-9223372036854775808

Conclusion

In this Java Tutorial, we learned about Java Math.round() function, with example programs.