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This article mainly introduces why the null pointer is abnormal, the article is very detailed, has a certain reference value, interested friends must read it!

Null pointer exception reasons: 1, no instantiation of the object out of new, or go to the database to query an empty object; 2, the object is null in the case of calling the object owned by the method or member variables.

The cause of null pointer exception

1. Do not instantiate the object from your new, or query an empty object in the database, which is a null pointer.

2. The exception NullPointer of the null pointer is caused by calling the methods or member variables owned by the object if the object is null.

Solution:

When calling a variable that may be null, it is best to make a non-null judgment.

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