Introduction to commonly used APIs and Math classes in Java (code examples)

This article brings you an introduction to commonly used APIs and Math classes in Java (code examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Overview of API

API——Application Programing Interface: Application programming interface is some predefined functions provided by java;

Purpose: To quickly write programs based on API, you only need to understand its functions without paying attention to the source code.

How to learn the API: first understand the overview and functions of the API, then look at the constructor to understand how to create and use the class, and finally look at the method to understand how to call it.

2. Numerical operation Math class

1. Overview

comes from the java.lang package (core package, provides A class that is crucial to the design of the Java programming language and can be used directly without import);

The Math class contains methods for performing basic numerical operations, such as basic exponentials, logarithms, square roots, and trigonometric functions

public final class extends Object

2. No constructor method

3. Main method

static double abs(double a) The return value is the absolute value of double

static double acos(double a) Returns the arc cosine of double

static double log(double a) Returns the natural logarithm of double (e Base)

static double log10(double a) Returns the base 10 logarithmic value of double

static int max(int ​​a, int b) Returns the maximum of two int values

static double random() Returns a double type value of [0,1)

Round up: static double floor(double a) Returns the largest double type integer less than or equal to a ;

Round down: static double ceil(double a) Return the smallest integer that is less than or equal to a

statisc String round(double a) Return the closest parameter Of long type, rounded

4. Fields and class variables

static double E Double value, equivalent to e, the base of natural logarithms

static double PI Double value, equivalent to pi, the ratio of the circumference of a circle to its diameter

5. Demonstration case

public class MathTest {
    public static void main(String[] args) {
        double a = -0.5;
        double pi = Math.PI;
        double e = Math.E;
        System.out.println("a的绝对值为：" + Math.abs(a));
        System.out.println("pi的反余弦值为：" + Math.acos(pi/4));
        System.out.println("a向上取整的值为：" + Math.floor(a));
        System.out.println("a向下取整的值为：" + Math.ceil(a));
        System.out.println("e的自然对数为" + Math.log(e));
        System.out.println("a与0.5中的最大值为：" + Math.max(a,0.5));
        System.out.println("a乘以一个[0,1)随机值为" + Math.random()*a);
        System.out.println("最接近a的long类型值为：" + Math.round(a));
        System.out.println("pi/6的正弦值为：" + Math.sin(pi/6));
    }
}

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