如何在运行时替换类？

Question

I have 2 classes. I want to replace one, class A so that ANY instance of it will actually behave like class B .

class A {
    fun test() = "a"
}

class B { 
    fun test() = "b"
}

I was trying to use the ClassLoader to do this but I couldn't get the system to call MyClassLoader .

class MyClassLoader() : ClassLoader() {

    @Throws(ClassNotFoundException::class)
    override fun loadClass(name: String): Class<*>? {
        if (name == "com.myapp.A") {
            return B::class.java
        } else return super.loadClass(name)
    }
}

This has to happen at compile time or runtime because I cannot manually replace every instance of A for B . (This is a minimalist example of the problem). A cannot be removed, this is a requirement.

So how do I attach MyClassLoader so that the system uses it?

I tried: Thread.currentThread().setContextClassLoader(MyClassLoader()) but the MyClassLoader doesn't get called.

Answer 1

i do not know what it will use for but for low scale ,you can try to have only on object that contain the methods and properties of both classes like example

val classType2 = 1
class AB{
    fun testA() = "a"
    fun testB() = "b"
    val classType1 = 1 

   fun test() {
     if(classType1 ==1){testA()}
     else{testB()}    
   }

}

you can add fun to change the class type or,

if you want to change all instances at the same replace classType1 with classType2 at if contition then change value of classType2.

i hope that

Answer 2

You can use the Factory design pattern. Depending on what kind of class instance you want you can load/return it at runtime from the Factory class static method.