Object comparison in Java

Code master 2021-01-21 11:21:31
object comparison java


One 、 Comparison of objects

Before, if it was a comparison of two values “==”, If it's a string comparison, it's usually used “equals()" Method , The method is String Class itself , How can we compare the objects of our custom class , If you use “==” Comparison compares the address information of two objects , But we normally think that all attribute values of two objects are equal, and two objects are equal .

DEMO: Compare the objects of a custom class

 
 
 
 

The above can realize object comparison , But it's implemented in the main method , General requirements The logical business code should be avoided as far as possible , The main method is a client , It's better to leave the process of comparison to Dept Class to complete .

DEMO: stay Dept Methods are defined in to realize the comparison of objects

 
 
 
 
 

The above code may be compared with the object itself , This kind of code is meaningless , So the code needs to be improved .

DEMO: Prevent the object from comparing itself with itself

 

There are still problems with the above code , The object that may be compared is an empty object , So there is a null pointer exception , So the code needs to be improved .

DEMO: Prevent comparison of empty objects

 
 

summary :

1、 The comparison of custom objects is meaningful only when two objects are created by the same class .

2、 When comparing, we should judge whether it is an empty object .

3、 When comparing, we should judge whether the object is compared with ourselves .

 

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