JvmField, JvmName, JvmOverloads, JvmStatic

Foo.kt

package ru.maksim.sample

class Foo {

    @JvmField
    val a = 1

    @JvmName("getStr")
    fun getB() = a.toString()

    @JvmOverloads
    fun bar(
        k: Int = -1,
        l: String = "abc",
        m: Int = 1,
    ) {
        println("k = $k, l = $l, m = $m")
    }

    companion object {

        @JvmStatic
        val CONST = 1

        @JvmStatic
        fun baz() {
            println("baz")
        }
    }
}

SampleJavaTest.java

package ru.maksim.sample;

import org.junit.jupiter.api.Test;

public class SampleJavaTest {

    @Test
    public void test() {
       final Foo foo = new Foo();
       foo.bar(1);
       foo.getStr();
       Foo.Companion.baz();
       Foo.baz();
       System.out.println(Foo.getCONST());
    }
}

SampleKotlinTest.kt

package ru.maksim.sample

import org.junit.jupiter.api.Test

class SampleKotlinTest {

    @Test
    fun foo() {
        val foo = Foo()
        foo.getB()
    }
}