In what scenarios does the NoSuchMethodError exception in Java occur?

In the Java programming process, the NoSuchMethodError exception is a common error type. It means that the code attempts to call a method or interface that does not exist, causing an error in the program.

NoSuchMethodError exception mainly occurs in the following scenarios:

1. Version upgrade: When the code uses a certain method, the definition of the method is upgraded from the old version to the new one version, but the code is not updated accordingly, causing the calling method to fail. This scenario mainly occurs when developers upgrade dependent libraries.
2. Type conversion: During type conversion, if it is found that the method to be converted does not exist in the type owned by the type before conversion, a NoSuchMethodError exception will be thrown. This situation may be due to a type conversion error, such as converting an object to an unrelated class.
3. Reflection call: Use Java's reflection mechanism to call a method, but the method does not exist in the class or the access rights are insufficient, a NoSuchMethodError exception will be thrown. In this case, you need to check whether the method name of the reflection call and the method parameter type and number are correct.
4. Class loading: When the class loader loads a class, if it is found that there are duplicate method definitions in the class and the type signatures are inconsistent, it will also cause the NoSuchMethodError exception to occur.

In order to avoid the occurrence of NoSuchMethodError exceptions, developers need to pay attention to the following aspects:

1. Version control: When upgrading dependent libraries, you need to pay attention to version compatibility and check whether it is necessary Update the original code.
2. Type conversion: When type conversion, you need to ensure that the type being converted has the method that needs to be called.
3. Reflection call: When using the reflection mechanism, you need to check whether the called method exists and whether you have access permissions.
4. Class loading: Avoid defining duplicate methods in the class and ensure that the type signatures of the methods are consistent.

In short, in programming, you need to test the code where NoSuchMethodError exception may occur multiple times to ensure the correctness of the code. If an exception occurs, it needs to be eliminated and repaired in a timely manner to ensure the normal operation of the program.

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