如果只初始化了超类对象，是否可以调用子类特定的方法？

Question

让我们从一个非常简单的例子中推断出来：a类：

public class a{
public a{}

子类b继承A：

public class b inherits a{
public b{super}
public void customMethodB(){}

public class c inherits a{
public c{super}
public void customMethodC(){}

public class Main{
public static void main(String[] args){
a newObject = null;
//User can now choose through input if he wants to create b or c. Lets say he creates b:
newObject = new b();
//His choice is stored in a string.
String userChoice = b;
//I now call the general object from another method for the user to interact with.
//(I have a feeling it is here my problem is).
}

userInteraction(a newObject, String userChoice){
if (userChoice.equals("b"){
newObject.customMethodB();
}
else if (userChoice.equals("c"){
newObject.customMethodC();
}

Answer 1

您的方法customMethodB在类型A中不存在。为了调用此方法，您必须强制转换对象（这里可以向下强制转换）

if (userChoice.equals("b") && newObject instanceof b){
((b)newObject).customMethodB();
}