is Object instance of MyClass

Question

I need to make equals function for MyClas.

public class MyClass
{
boolean equals(Object value)
  {
    if (... value is type of MyCLass ...)
      {
        return= ... check conditions...;
      } else return false;
  }
}

For this purpose I need to know if value of Object is type of MyClass. How to make it?

it always shocks me that people care enough to answer you a full good answer but don't think the question is good enough to give upvote. +1 for good question — No Idea For Name, Aug 29 '13 at 12:58
possible duplicate of [Any reason to prefer getClass() over instanceof when generating .equals()?](http://stackoverflow.com/questions/596462/any-reason-to-prefer-getclass-over-instanceof-when-generating-equals) — Raedwald, Apr 15 '15 at 20:04

score 5 · Accepted Answer · answered Aug 29 '13 at 12:47

5

In order to check if value is of type MyClass use:

 if( value instanceof MyClass)

answered Aug 29 '13 at 12:47

BobTheBuilder

18,858
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Not recommended: http://stackoverflow.com/questions/596462/any-reason-to-prefer-getclass-over-instanceof-when-generating-equals – Raedwald Apr 15 '15 at 20:03

score 1 · Answer 2 · answered Aug 29 '13 at 12:47

1

instanceof operator is used to determine that. It's infix, so use it like so...

(value instanceof MyClass)

answered Aug 29 '13 at 12:47

alex

479,566
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984

score 1 · Answer 3 · answered Aug 29 '13 at 12:48

1

    public class MyClass
    {
       boolean equals(Object value)
      {
           if (value instanceof  MyCLass)
           {
              return= ... check conditions...;
           } else return false;
       }
   }

answered Aug 29 '13 at 12:48

Prabhakaran Ramaswamy

25,706
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score 1 · Answer 4 · answered Aug 29 '13 at 12:50

You can do

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    MyClass myClass = (MyClass) o;
    //Your logic

You can also use instanceof instead of getClass() approach.

score 1 · Answer 5 · answered Aug 29 '13 at 12:54

Just a little IDE trick. Just to save up some time.

In eclipse you can do that by right click on the class file and select source --->generate hashCode() and equals() method , select all the attribute you need to compare and IDE will generate corresponding code for you

An excerpt

public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Employee other = (Employee) obj;
        if (firstName == null) {
            if (other.firstName != null)
                return false;
        } else if (!firstName.equals(other.firstName))
            return false;
        if (id != other.id)
            return false;
        if (lastName == null) {
            if (other.lastName != null)
                return false;
        } else if (!lastName.equals(other.lastName))
            return false;
        if (salary != other.salary)
            return false;
        return true;
    }

score 0 · Answer 6 · answered Aug 29 '13 at 12:52

0

value instanceof ClassName

the instanceof key word checks, where value is a subclass of ClassName, If yes reutns true and otherwise returns false

answered Aug 29 '13 at 12:52

Suresh Atta

120,458
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score 0 · Answer 7 · answered Aug 29 '13 at 13:00

Altough RTTI (Real Time Type Identification) is considered a code smell by some individuals, there are two alternatives, one is to use the instanceof operator:

if(value instanceof MyClass)

On the other hand, you can use a full fledged method from the Class class, that given two objects, you can determine if they belong to the same hierarchy (much more powerful than instanceof IMO):

if(value.getClass().isAsignableFrom(getClass()))

This second approach determines if value is the very same class or a superclass/superinterface of the current class (the this) at execution time given any kind of object. This is where isAsignableFrom excels, since with instanceof you need to know the reference type at compile time.

is Object instance of MyClass

7 Answers7