Cannot invoke "java.util.ArrayList.size()" because "go" is null
时间: 2023-12-11 17:46:26 浏览: 50
这个错误提示意味着你在一个空的 ArrayList 上调用了 size() 方法。你需要确保 ArrayList 已经初始化了,也就是赋值了数组对象。比如,如果你定义了一个 ArrayList 变量,你需要在使用它之前先实例化它,例如:
```
ArrayList<String> list = new ArrayList<>();
```
然后你就可以使用 ArrayList 上的 size() 方法了,例如:
```
int size = list.size();
```
如果你还是遇到这个错误,可以检查一下你的代码是否在调用 size() 方法之前正确地初始化了 ArrayList。
相关问题
Cannot invoke "java.util.ArrayList.isEmpty()" because "list" is null
This error message means that you are trying to call the isEmpty() method on an ArrayList object that is null, meaning it has not been initialized or assigned to any value. It is important to make sure that you have properly initialized the ArrayList object before calling any of its methods.
To fix this error, you should first check if the ArrayList object is null before calling the isEmpty() method. You can do this using an if-statement:
```
if (list != null && !list.isEmpty()) {
// list is not null and not empty, do something
} else {
// list is null or empty, handle the error
}
```
Alternatively, you can initialize the ArrayList object with an empty list when you declare it:
```
ArrayList<String> list = new ArrayList<>();
```
This way, even if you forget to add any elements to the list, it will not be null and you can call its methods without any errors.
Cannot invoke "java.util.ArrayList.iterator()" because "list" is null怎么解决
这个错误提示说明 `list` 对象为 `null`,导致无法调用 `iterator()` 方法。需要在使用 `list` 对象之前,先对其进行非空判断。
可以使用如下代码进行判断:
```
if (list != null) {
for (Book bi : list) {
String id = bi.getId();
// 其他操作
}
} else {
// 处理 list 为 null 的情况
}
```
这样就可以避免出现 `NullPointerException` 异常。
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