Question

我想能够说出一个此类的实例并提供一个类型，然后代码可以实例化该类的新实例。

fun maker(type: Class<Animal>): Animal {
    if(type == Class<Dog>) {
       return Dog()
    } 
    else if (type == Class<Cat>) {}
    ...
}

执行此操作的好方法是什么？

Answer 1

如果它们都具有零参数构造函数，则可以执行以下操作：

SettingWithCopyWarning

您可以使其返回传入的类型，以实现更多用途：

fun maker(type: Class<Animal>): Animal {
    return type.newInstance()
}

Answer 2

遵循您的示例的正确版本（不确定总体上最佳方法）：

import numpy as np

# oddly enough - numpy doesn't have it's own ffill function:

def np_ffill(arr):
    mask = np.arange(len(arr))
    mask[np.isnan(arr)]=0
    np.maximum.accumulate(mask, axis=0, out=mask)
    return arr[mask]


t1=np.ceil(t1).astype("int")
t2=np.ceil(t2).astype("int")
r1=np.empty(max(t1)+1)
r2=np.empty(max(t2)+1)
r1[:]=np.nan
r2[:]=np.nan
r1[t1]=m1
r2[t2]=m2

r1=np_ffill(r1)
r2=np_ffill(r2)

>>> print(r1,r2)

[0.4 0.4 0.4 0.6 0.6 0.6 0.2] [1.  1.  1.  1.  1.4 1. ]

#in order to get avg:

r3=np.vstack([r1[:len(r2)],r2[:len(r1)]]).mean(axis=0)

>>> print(r3)
[0.7 0.7 0.7 0.8 1.  0.8]

然后创建对象：

fun <T: Animal> maker(type: Class<T>): T? {
    return when (type) {
      Cat::class.java -> Cat() as T
      Dog::class.java -> Dog() as T
      else -> null
    }
}

Answer 3

（已更新）我不是Kotlin专家，但是您可以执行以下操作：

import kotlin.reflect.KClass
import kotlin.reflect.full.createInstance

class A {
    fun greet() {
        println("Hello A");
    }
}

class B{
    fun greet() {
        println("Hello B");
    }
}

fun <T : Any> maker(clazz: KClass<T>): T {
    return clazz.createInstance();
}

val aObj = maker<A>(A::class);
aObj.greet();

val bObj = maker<B>(B::class);
bObj.greet();

输出：

Hello A
Hello B

我希望现在您只需要将类传递给方法并返回一个对象就可以了。

因为您将使用Animal作为父类，所以可以替换Any => Animal

fun <T : Animal> maker(clazz: KClass<T>): T {
    return clazz.createInstance();
}

Answer 4

如果函数可以为import com.ghgande.j2mod.modbus.facade.ModbusSerialMaster; import com.ghgande.j2mod.modbus.Modbus; import com.ghgande.j2mod.modbus.ModbusException; import com.ghgande.j2mod.modbus.procimg.Register; import com.ghgande.j2mod.modbus.util.SerialParameters; public class ModbusMaster { /** * @param args */ public static void main(String[] args) { /* The important instances of the classes mentioned before */ ModbusSerialMaster serialMaster = null; // the connection /* Variables for storying the parameters */ String portname = "COM3"; // the name of the serial port to be used int unitID = 1 ; // the unit identifier we will be talking to int startingRegister = 10001; // the reference, where to start reading from int registerCount = 0; // the count of the input registers to read Register[] slaveResponse = new Register[registerCount]; try { /* Setup the serial parameters */ SerialParameters parameters = new SerialParameters(); parameters.setPortName(portname); parameters.setBaudRate(9600); parameters.setDatabits(8); parameters.setParity("None"); parameters.setStopbits(1); parameters.setEncoding(Modbus.SERIAL_ENCODING_RTU); parameters.setEcho(false); /* Open the connection */ serialMaster = new ModbusSerialMaster(parameters); serialMaster.connect(); } catch (Exception exception) { System.out.println("Not Run"); exception.printStackTrace(); } /* Read the first four holding registers */ try { slaveResponse = serialMaster.readMultipleRegisters(unitID, startingRegister, registerCount); for (int i = 0; i < slaveResponse.length; i++) { System.out.println("reg" + i + " = " + slaveResponse[i]); } } catch (ModbusException e) { e.printStackTrace(); } /* Close the connection */ serialMaster.disconnect(); } }，则也可以使用reified类型

com.ghgande.j2mod.modbus.ModbusIOException: I/O exception - failed to read
    at com.ghgande.j2mod.modbus.io.ModbusRTUTransport.readResponse(ModbusRTUTransport.java:645)
    at com.ghgande.j2mod.modbus.io.ModbusSerialTransaction.execute(ModbusSerialTransaction.java:189)
    at com.ghgande.j2mod.modbus.facade.ModbusSerialMaster.readMultipleRegisters(ModbusSerialMaster.java:269)
    at ModbusMaster.main(ModbusMaster.java:53)

请注意，要使用inline，该类必须具有no-arg构造函数，否则将抛出inline fun<reified T: Animal> make() = T::class.createInstance() ... val dog = make<Dog>()

如何通过传递类型来创建类的实例

4 个答案: