this in equals method

Question

I am looking at the equals method  and I see this and I don t understand what it means   I do understand them when I see it in constructors and some methods but its not clear to me when they are in equals method something like this    obj    this     what does this mean here   where does it come from    I understand when it says something like this name   name   from a method like this   Override public boolean equals Object obj        if  obj    this            return true            if  obj    null    obj getClass      this getClass              return false          sorry it might be a duplicate but I couldnt find anything

User · Answer

this refers to the current instance of the class  object  your equals-method belongs to  When you test this against an object  the testing method  which is equals Object obj  in your case  will check wether or not the object is equal to the current instance  referred to as this    An example   Object obj   this  this equals obj     true   Object obj   this  new Object   equals obj     false

User · Answer

You have to look how this is called   someObject equals someOtherObj     This invokes the equals method on the instance of someObject  Now  inside that method   public boolean equals Object obj      if  obj    this      is someObject equal to obj  which in this case is someOtherObj      return true   If so  these are the same objects  and return true       You can see that this is referring to the instance of the object that equals is called on  Note that equals   is non-static  and so must be called only on objects that have been instantiated   Note that    is only checking to see if there is referential equality  that is  the reference of this and obj are pointing to the same place in memory  Such references are naturally equal   Object a   new Object    Object b   a    sets the reference to b to point to the same place as a Object c   a    same with c b equals c    true  because everything is pointing to the same place   Further note that equals   is generally used to also determine value equality  Thus  even if the object references are pointing to different places  it will check the internals to determine if those objects are the same   FancyNumber a   new FancyNumber 2    Internally  I set a field to 2 FancyNumber b   new FancyNumber 2    Internally  I set a field to 2 a equals b    true  because we define two FancyNumber objects to be equal if their internal field is set to the same thing

User · Answer

this is the current Object instance  Whenever you have a non-static method  it can only be called on an instance of your object

User · Answer

You are comparing two objects for equality   The snippet   if  obj    this        return true      is a quick test that can be read       If the object I m comparing myself to is me  return true      You usually see this happen in equals methods so they can exit early and avoid other costly comparisons

[java] this in equals method

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