我为什么要在Java中调用super()? [英] Why should I call super() in Java?
问题描述
我在一本关于java的书中看到了一个例子:
I see an example from a book that I read about java:
public class A{
public A(){
System.out.println("A");
}
}
public class B extends A{
public B(){
super();
System.out.println("B");
}
public static void main(String[] args){
B b = new B();
}
}
我不明白为什么要 super()
在这儿?即使我删除 super()
,我也会得到相同的结果(A会被打印,然后是B)。据我所知,当我初始化子类时,父类在它之前初始化。那么为什么要使用 super()
?
I can't understand why should super()
be here? Even if I delete super()
, I would get the same result (A would be printed, and then B). As I understand, when I initialize the subclass, then the parent class is initialize before it. So why use super()
?
推荐答案
在这种特殊情况下,你不需要调用 super();
,因为Java将隐式地插入对 super();
的调用在构造函数中,如果您没有显式调用它。 ( Java Tutorial link)。
In this particular case, you don't need to call super();
, because Java will insert the call to super();
implicitly in a constructor if you don't explicitly call it. (Java Tutorial link).
只有在其他情况下才需要调用超类中的另一个非默认构造函数,例如:
It only becomes necessary in other cases, in which you want to call another, non-default constructor in the superclass, such as this:
public class A{
public A(String s){
System.out.println("A");
}
}
public class B extends A{
public B(String s){
super(s);
System.out.println("B");
}
}
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