nullpointexception
时间: 2024-05-06 07:20:35 浏览: 8
NullPointerException is a common exception in Java that occurs when we try to access an object or variable which is null. In simple terms, it means that we are trying to perform an operation on a null reference.
For example, consider the following code snippet:
```java
String str = null;
System.out.println(str.length());
```
In this code, we are trying to access the length of the variable `str`, which is null. Hence, it will throw a NullPointerException at runtime.
To avoid such exceptions, we need to check if the object or variable is null before using it in our code. We can do this using an if statement or by using Java's built-in null-checking features, such as the `Objects.requireNonNull` method.