What are precautions for implementing java. Lang. Object. Equals (object?

If all objects in the world are judged by direct equals, it will be okay. There are always some situations:

• Objects are placed in containers (such as hashset), and then equals is judged;
• Perform equals judgment between the object and the subclass of the inherited object;
• ......

 

[1] an incorrect equals method signature is defined.

No: Public Boolean euqals (pointer O );

Yes: Public Boolean equals (ObjectO );

 

[2] The equals method is reloaded, but the hashcode method is not reloaded at the same time.

No: No hashcode ()

Yes: Public intHashcode (){Return (41*(41 + getx () + Gety ());}

 

[3] equals definition based on changing word Fields

No: Public int;

Yes: PublicFinalInt;

 

[4] equals error definitions that do not meet the equivalence relationship

No: direct parent and sub-object comparison;

Yes: & this.Getclass ().Equals (that. getclass ())

 

 

Learning:

Http://blog.csdn.net/haoel/article/details/4282239

Http://www.artima.com/lejava/articles/equality.html