[英]Why can't I have an private abstract method?
假设我有我的经典作品:
public abstract class Mammal {
private int numLegs;
private String voice;
private Coat coat;
public abstract void eat();
public abstract void speak();
public abstract void sleep();
private abstract void ingestFood(Food f); //The abstract method ingestFood in type Mammal can only set a visibility modifier, one of public or protected
}
通过这些具体的实现:
public class Dog extends Mammal {
private int numLegs = 4;
private String voice = "Woof!";
private Coat coat = new Coat(COATTYPE.FUR, COATCOLOR.BROWN);
@Override
public void eat()
{
Rabbit r = chaseRabbits();
if (r != null) ingest(r);
else {
Garbage g = raidBin();
if (g!= null) ingest(g);
}
}
@Override
private void ingest(Food f)
{
gobbleItAllUpInFiveSeconds(f);
stillFeelHungry();
}
}
public class Human extends Mammal {
private int numLegs = 2;
private String voice = "Howdy!!";
private Coat coat = new Coat(COATTYPE.SKIN, COATCOLOR.PINK);
@Override
public void eat()
{
Food f = gotoSuperMarket();
ingest(f);
}
@Override
private void ingest(Food f)
{
burp();
}
}
现在,我想要Mammal
类中所有哺乳动物实例都可以调用的方法,例如
public String describe() {
return "This mammal has " + this.numLegs + "legs, a " + this.coat.getColor() + " " this.coat.getCoatType() + " and says " + this.voice;
}
我的问题是,通过使Mammal
类不抽象,是否有可能独自创造出哺乳动物? 例如
Mammal me = new Mammal();
您不应该能够这样做。
但是,我确实希望有一些公共方法,这些方法由所有子类都调用的父类实现,但是每个子类都调用自己的私有方法。
您完全可以在抽象类中实现方法:
“抽象类类似于接口。您不能实例化它们,并且它们可能包含使用或不使用实现声明的方法的混合。”
https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html
回答标题中的问题(“ 为什么不能有私有的抽象方法? ”):
您不能拥有private abstract
方法,因为abstract
方法需要在子类中实现。 但是private
方法在子类中不可见。
(如果您想要一个仅在子类中可见而不在公共场合可见的方法,则需要将这些方法设置为protected
)
因此,您永远无法实现private abstract
方法。 这就是Java不允许使用它们的原因-它们没有意义。
如果希望未实现的方法在子类上表现不同,则将它们声明为抽象方法,并且要继承的方法使它们像普通方法一样。 还可以使用protected而不是private来继承类的访问:
public abstract class Mammal
{
protected int numLegs;
protected String voice;
protected Coat coat;
abstract void eat();
abstract void speak();
abstract void sleep();
public String describe()
{
return "This mammal has " + this.numLegs + "legs, a "
+ this.coat.getColor() + " " this.coat.getCoatType() + " and says " + this.voice;
}
}
并使用构造函数初始化变量并实现抽象方法:
public class Dog extends Mammal
{
public Dog(){
this.numLegs = 4;
this.voice = "Woof!";
this.coat = new Coat(COATTYPE.FUR, COATCOLOR.BROWN);
}
void eat(){
System.out.println("eating like a dog");
}
void speak(){
System.out.println("speaking like a dog");
}
void sleep(){
System.out.println("sleeping like a dog");
}
}
public class Human extends Mammal
{
public Human(){
this.numLegs = 2;
this.voice = "Howdy!!";
this.coat = new Coat(COATTYPE.SKIN, COATCOLOR.PINK);
}
void eat(){
System.out.println("eating like a human");
}
void speak(){
System.out.println("speaking like a human");
}
void sleep(){
System.out.println("sleeping like a human");
}
}
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.