英文:
What is the difference between creating an object with superclass reference and creating an object with subclass reference?
问题
以下是要翻译的代码部分：
class C implements Runnable{
public void run() {
for(int i=0;i<5;i++) {
System.out.println("Thread2");
try {
Thread.sleep(1000);
} catch (Exception e) {}
}
}
}
然后在我的主线程中，我写下：
C c = new C();
它产生的输出与以下代码相同：
Runnable c=new C();
关于它们各自的优点以及何时使用哪一个，有没有通用的规则呢？
英文:
Here's a snippet of my code:
class C implements Runnable{
public void run() {
for(int i=0;i<5;i++) {
System.out.println("Thread2");
try {
Thread.sleep(1000);
} catch (Exception e) {}
}
}
}
Then in my main thread, I write:
C c = new C();
which produces the same output as
Runnable c=new C();
What are the advantages of using either of them?
Is there a general rule when to use which one?
答案1
得分: 1
对于C c = new C()，变量的类型是C类型，而对于Runnable c = new C()，变量的类型是Runnable。对于第一种情况，只能存储C类型的实例在变量中。对于第二种情况，允许存储实现了Runnable接口的类的实例。
Runnable是一个函数式接口，用于将可运行的代码片段作为参数传递给方法。通常，对于函数式接口，你总是会使用第二种情况。
英文:
For C c = new C(), the type of the variable is of type C, whereas with Runnable c = new C(), the type of the variable is Runnable. For the first case, only instances of type C can be stored in the variable. For the second case, instances of a class that implements Runnable are allowed.
Runnable is a functional interface that is used to pass pieces of runnable code as parameters to methods. Usually, you're always going to use the second case for functional interfaces.
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