如何在java子类中添加两个变量作为一个变量传递给超类？

Question

我只是在学习Java，我有一个问题。我不确定我是否使用了正确的术语，所以如果需要的话请纠正我。我很好奇是否有更好的方法来增加前爪和后爪，把它们传递给动物类。这样做是可行的，但我在寻找我想要做的事情时遇到了困难，这使得我很难弄清楚我是否做错了。这是我正在工作的子类。

public class Bear extends Animal // This is a Bear class, it is a subclass of Animal.
{
  private int frontClaws; // This is an instance variable for front claws.
  private int backClaws;  // This is an instance variable for back claws.
  public Bear (String name, int fC, int bC) // This is the Bear constructor.
  {
    super (name, fC + bC); // This passes the name and the sum 
                           // of the claws to the Animal's constructor

    frontClaws = fC;  // not sure why this has to be done, 
                      // and frontClaws + backClaws can't be used directly. Because they are private?
    backClaws = bC;   // Same as confusion as above.
   }
    public void print()  // This calls the print method.
   {
    super.print();    // This calls the print method from 
                      // Animal and prints the args from Animal 
                      // as well as the args from Bear.
    System.out.println("- " + frontClaws + " Front Claws, and " + backClaws + " Back Claws.");
   }
}

提前感谢！

tc

Answer 1

在调用超类构造函数之前，您不能访问字段--基本上，任何构造函数所做的第一件事就是调用超类构造函数。唯一要做的事是计算参数，以调用超类构造器--在您的例子中，这涉及到fC和bC之和。

基本上，假设您需要Animal来得到frontClaws和backClaws之和，这看起来是一个合理的实现。

Answer 2

1.

super (name, fC + bC); // This passes the name and the sum 
                           // of the claws to the Animal's constructor

是构造函数的第一行(必须如此)，因为其中的第1条指令总是对超类构造函数的调用。

这将引发错误：

public Bear (String name, int fC, int bC) // This is the Bear constructor.
  {
    frontClaws = fC;  
    backClaws = bC;  
    int totalClaws = fC + bC;
    super (name, totalClaws );
   }

error: call to super must be first statement in constructor

2.

frontClaws = fC;  // not sure why this has to be done, 
                      // and frontClaws + backClaws can't be used directly. Because they are private?
    backClaws = bC;   // Same as confusion as above.

因为他们是私人的？

您基本上是从构造函数中初始化它们，以便将它们传递给超类的构造函数。如果不是这样的话，那么您可以通过setter方法来选择它们的初始化。