Question

我在将对象放入链接列表时遇到问题。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]);

但是我收到错误：

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

Empty（）是Fish and Shark的超类。

以下是循环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++;
}

以下是节点的代码：公共类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，我是OOP的新手。有什么建议吗？

Answer 1

当我们按如下方式声明变量时 -

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

该变量是声明它的块（{}）的本地变量。并且在那个街区外面看不到它。

你正试图在外面使用它 -

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

不可见的地方。所以，编译器抱怨。

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]);

传递不同类Java的对象

1 个答案: