Cannot invoke "java.util.Stack.push(Object)" because "this.InStack" is null

当报错提示"Cannot invoke 'java.util.Stack.push(Object)' because 'this.InStack' is null"时，表示在调用Stack类的push方法时，Stack对象为空。这可能是由于未对Stack对象进行初始化或者初始化后被赋值为null所导致的。请检查是否在使用push方法之前正确初始化了Stack对象，并确保对象不为null。

相关问题

Exception in thread main java.lang.NullPointerException: Cannot invoke java.util.List.add(Object) because this.WorkerAL is null

这个错误是因为你在尝试向一个空的列表中添加元素，导致了空指针异常。你需要在使用 `add()` 方法之前，先初始化这个列表，即创建一个新的 `ArrayList` 对象，如下所示：

List<Object> WorkerAL = new ArrayList<Object>();

或者检查一下这个列表是否在其他地方被正确地初始化了。

Cannot invoke "java.util.HashMap.put(Object, Object)" because "this.scoreMap" is null

This error occurs when you are trying to invoke the `put` method on a `HashMap` object that has not been initialized. It means that the reference to the `scoreMap` object is null and therefore cannot be used to call the `put` method.

To fix this error, you need to initialize the `scoreMap` object before using it. You can do this by creating a new instance of the `HashMap` class and assigning it to the `scoreMap` reference, like this:

scoreMap = new HashMap<>();

This will create a new empty `HashMap` object and assign it to the `scoreMap` reference, allowing you to use the `put` method to add key-value pairs to the map.