Kotlin实现适配器模式时出现getter方法getRadius重复命名报错问题

Exception in thread "main" java.lang.ClassFormatError: Duplicate method name "getRadius" with signature "()I" in class file RoundHole
 at java.lang.ClassLoader.defineClass1 (ClassLoader.java:-2) 
 at java.lang.ClassLoader.defineClass (ClassLoader.java:756) 
 at java.security.SecureClassLoader.defineClass (SecureClassLoader.java:142) 

Kotlin 为主构造函数中声明的val属性默认生成与属性名对应的getter方法，你在实现WorkingWithRound接口的RoundPeg、RoundHole类中，同时存在两种getRadius()的实现：

• 主构造参数val radius自动生成的getRadius()
• 手动重写的override fun getRadius() = radius
  两个方法签名完全一致，JVM加载类时检测到重复方法触发报错。

提供两种可直接运行的改法：

改法1：适配Kotlin语法习惯，用属性实现接口 #

interface WorkingWithRound {
    val radius: Int
}

open class RoundPeg(override val radius: Int = 0): WorkingWithRound

class RoundHole(override val radius: Int = 0): WorkingWithRound {
    fun fit(peg: RoundPeg) {
        println(radius >= peg.radius)
    }
}

class SquarePeg(val width: Int = 0)

class SquarePegAdapter(val speg: SquarePeg): RoundPeg() {
    override val radius: Int
        get() = (speg.width / 2 * 1.4).toInt()
}


fun main() {
    val hole = RoundHole(5)
    val rpeg = RoundPeg(5)
    hole.fit(rpeg) // 输出true

    val small_sqpeg = SquarePeg(5)
    val large_sqpeg = SquarePeg(10)

    val small_sqpeg_adapter = SquarePegAdapter(small_sqpeg)
    val large_sqpeg_adapter = SquarePegAdapter(large_sqpeg)
    
    hole.fit(small_sqpeg_adapter) // 输出true
    hole.fit(large_sqpeg_adapter) // 输出false
}

改法2：不修改原有接口定义，规避自动生成getter冲突 #

interface WorkingWithRound {
    fun getRadius(): Int
}

// 主构造参数加private，避免自动生成public的getRadius方法
open class RoundPeg(private val radius: Int = 0): WorkingWithRound {
    override fun getRadius() = radius
}

// 主构造参数加private
class RoundHole(private val radius: Int = 0): WorkingWithRound {
    override fun getRadius() = radius
    
    fun fit(peg: RoundPeg) {
        println(getRadius() >= peg.getRadius())
    }
}

class SquarePeg(val width: Int = 0)

class SquarePegAdapter(val speg: SquarePeg): RoundPeg() {
    override fun getRadius() = (speg.width / 2 * 1.4).toInt()
}


fun main() {
    val hole = RoundHole(5)
    val rpeg = RoundPeg(5)
    hole.fit(rpeg)

    val small_sqpeg = SquarePeg(5)
    val large_sqpeg = SquarePeg(10)

    val small_sqpeg_adapter = SquarePegAdapter(small_sqpeg)
    val large_sqpeg_adapter = SquarePegAdapter(large_sqpeg)
    
    hole.fit(small_sqpeg_adapter)
    hole.fit(large_sqpeg_adapter)
}

内容的提问来源于stack exchange，提问作者Nero Nguyen