Java documentation interpretation: Detailed description of the round() method of the Math class

The Math class is a commonly used mathematics library in Java. It provides many commonly used mathematical functions and constants, such as trigonometric functions, exponential functions, constant π, etc. Among them, the round() method is one of the more commonly used methods in the Math class. This article will explain the round() method of the Math class in detail, including its usage, function and specific code examples.

1. Overview of the round() method

The round() method is a static method in the Math class. Its function is to round a floating point number to the nearest integer. The syntax of this method is as follows:

public static int round(float a)
public static long round(double a)

This method receives a parameter a of float type or double type and returns an integer of int type or long type. Among them, when the decimal part of a is less than 0.5, round a to get an integer; when the decimal part of a is greater than or equal to 0.5, add 1 to a and round off to get an integer.

2. Use of round() method

1. Round floating point numbers that do not require high precision

In some scenarios, we do not Floating point numbers need to be processed with high precision and only need to be rounded to an integer. At this point, we can use the round() method of the Math class to achieve this.

For example, we have a float type variable f, its value is 3.1415926, we want to round it to an integer, you can use the following code:

float f = 3.1415926f;
int result = Math.round(f);
System.out.println(result);

The running result is:

3

As can be seen from the result, 3.1415926 was rounded to 3.

Similarly, for a double type variable, you can also use the round() method of the Math class to round it to an integer. For example, we have a double type variable d, its value is 123.456789, we want to round it to an integer, you can use the following code:

double d = 123.456789;
long result = Math.round(d);
System.out.println(result);

The running result is:

123

From the result As can be seen, 123.456789 is rounded to 123.

2. Approximate processing of floating point numbers

In some scenarios, we need to perform some approximate processing of floating point numbers. For example, in computer simulations, the precision of floating point numbers is limited, and some floating point numbers may not be accurately represented. At this point, we can approximate the floating point number to get it closer to the correct value.

For example, we want to approximate a double type variable so that its floating point part only retains two decimal places. We can use the following code:

double d = 3.1415926;
double approx = Math.round(d * 100) / 100.0;
System.out.println(approx);

This code first multiplies d by 100, then uses the round() method to round it to an integer, and finally divides it by 100.0 to get an approximate value. The running result is:

3.14

As can be seen from the result, 3.1415926 is approximated to 3.14.

3. Notes on the round() method

1. If the parameter is infinite or NaN, the round() method will directly return the parameter itself.

For example, for a float type variable f, if its value is infinite or NaN, then Math.round(f) will directly return the parameter f itself. For example, for the following code:

float f = Float.POSITIVE_INFINITY;
int result = Math.round(f);
System.out.println(result);

The result will be output:

2147483647

Since Float.POSITIVE_INFINITY is positive infinity and cannot be represented in the computer, Math.round(f) directly returns f itself.

Similarly, for a double type variable d, if its value is infinite or NaN, then Math.round(d) will directly return the parameter d itself.

2. For cases where the parameters are too large or too small, the round() method may produce abnormal or unexpected results.

Due to the limitation of computer memory space, the round() method may produce abnormal or unexpected results for floating point numbers that are too large or too small. For example, for the following code:

double d = 1.23456789E308;
long result = Math.round(d);
System.out.println(result);

Since 1.23456789E308 exceeds the upper limit of the double type, this code will throw an exception.

Similarly, for floating point numbers that are too small, such as the following code:

double d = 1.23456789E-323;
long result = Math.round(d);
System.out.println(result);

Since 1.23456789E-323 is smaller than the precision limit of the double type, this code will return 0 instead of what is expected. approximate value.

4. Conclusion

Through the above code examples, we can see that the round() method of the Math class is a more practical mathematical method, which can conveniently round floating point numbers into integers. , and can approximate floating point numbers. However, when using this method, we need to pay attention to parameter ranges and precision requirements to avoid abnormal or unexpected results.

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