java - 传递不同类Java的对象

Question

我在将对象放入链表时遇到问题。这是代码:

if(runTypes[k]==EMPTY){
      Empty creature = new Empty();
    }
else if(runTypes[k]==FISH){
            Fish creature = new Fish();
        }
else if (runTypes[k]==SHARK){
            Shark creature = new Shark(starveTime);
        }
DLinkedList.insertEnd(creature,runLengths[k]);

但是我得到一个错误:

RunLengthEncoding.java:89: cannot find symbol
symbol  : variable creature
location: class RunLengthEncoding
        DLinkedList.insertEnd(creature,runLengths[k]);  
                              ^
1 error

Empty() 是 Fish 和 Shark 的父类(super class)。

下面是循环LinkedList类中insertEnd方法的代码:

public void insertEnd(Empty creature, int number) {
  DListNode3 node = new DListNode3(creature);
  head.prev.next = node;
  node.next = head;
  node.prev = head.prev;
  head.prev=node;
  node.amount = number;
  size++;
}

这是节点的代码: 公共(public)类 DListNode3 {

    public Empty creature;
    public DListNode3 prev;
    public DListNode3 next;
    public int amount;

    DListNode3(Object creature) {
        this.creature = creature;
        this.amount = 1;
        this.prev = null;
        this.next= null;
    }

    DListNode3() {
        this(null);
        this.amount = 0;
    }
    }

我不知道该怎么做，而且我是 OOP 的新手。有什么建议吗？

Answer 1

当你我们声明一个变量如下-

if(runTypes[k] == EMPTY) {
      Empty creature = new Empty();
}

该变量是声明它的 block ({}) 的本地变量。而且在那个街区之外是不可见的。

而你正试图在外面使用它 -

DLinkedList.insertEnd(creature,runLengths[k]);

看不见的地方。所以，编译器在提示。

您可以执行以下操作来解决问题 -

Empty creature = null; //Empty can be the variable type, it's the parameter type in the insertEnd method
if(runTypes[k] == EMPTY) {
     creature = new Empty(); //no problem, it's the same class
} else if(runTypes[k] == FISH) {
     creature = new Fish(); //no problem, Fish is a subclass
} else if (runTypes[k] == SHARK) {
     creature = new Shark(starveTime); //no problem, Shark is a subclass of Empty
}
DLinkedList.insertEnd(creature, runLengths[k]);