First, explain
Each class can correspond to a companion object
The members of the companion object are unique
Members of companion objects are similar to static members of Java

2, In Java
Methods calling the kotlin class need to add
@JvmStatic
To call the member variable of the kotlin class, you need to add
@JvmField

3, Like the math class in java.lang package
All its methods are static. When using, you can directly use math.xxx (method)

4, Like the method in the Integer class, this is used in Java

Integer a = Integer.valueOf(3);

5, In Kotlin, forms like this can be called directly

Take a look at the code

Integer a = Integer.valueOf(3);

6, Take a look at an example
Let's take a look at the classes in kotlin

package net.println.kotlin.chapter4

/**
 * @author:wangdong
 * @description:Companion objects and static members
 */

fun main(args: Array<String>) {
    //val a = minOf(args[0].toInt(),args[1].toInt())
    //Use the following definition
    val latitude = Latitude.ofDouble(40.3)
    val latitude2 = Latitude.ofLatitude(latitude)
    println(Latitude.TAG)
}

/**Define a latitude class*/
class Latitude private constructor(val value: Double){
    //Class
    companion object {
        //Define a static method
        @JvmStatic
        fun ofDouble(double: Double): Latitude {
            return Latitude(double)
        }
        //Define a static method
        @JvmStatic
        fun ofLatitude(latitude: Latitude): Latitude {
            return Latitude(latitude.value)
        }

        //Define a static variable
        @JvmField
        val TAG: String = "hello"
    }
}

Take a look at Java

package net.println.kotlin.chapter4;

/**
 * @author:wangdong
 * @description:Calling Latitude method in java
 */
public class StaticJava {

    Integer a = Integer.valueOf(3);

    public static void main(String[] args) {
        //You need to call the company to call the method
        Latitude latitude = Latitude.Companion.ofDouble(54.4);
        //You can add an annotation @ JvmStatic to the method in Latitude
        Latitude latitude2 = Latitude.ofDouble(54.87);
        System.out.println(Latitude.TAG);
    }

}

End