overriding equals and hashcode methods in java?

Question

I have below class.

Request.java

public class Request implements Serializable {

    private String id;
    private String name;
    private String hid;

    // getters and setters 

    // This class does not override any equals() and hashCode() methods
}

public class EmpRequest implements Serializable {
    private Request request;
    //Now here in this class I need override equals() and hashCode() methods based on **request**
}

In EmpRequest class, I need to override equals() and hashCode() based on properties of Request object.

If two request objects id is equal then i need to return true. If two objects ids are not equal then i need to check for name and hid properties. If name and hid properties of both the objects are equals then i need to return true. Else false

How can I do that? I tried overriding equals() and hashCode() but eclipse gave me below the warning.

The field type 'com.mycompany.Request' does not implement equals() and hashCode() - the resulting code may not work correctly.

At the same type I cannot modify Request class as I don't have control over it.

How can I write equals() and hashCode() considering above conditions?

@SachinPasalkar you should mind full when you put a comment. Any of your comment want help for OP. you can just leave here if you don't have any idea — Ruchira Gayan Ranaweera, Dec 12 '13 at 07:02
@SachinPasalkar I understand your rage and passion, but "Read java book first" is at best lame. — aquaraga, Dec 12 '13 at 07:03
http://stackoverflow.com/questions/20493208/overriding-hashcode-and-equals-method-in-java/20493800#20493800 — dev2d, Dec 12 '13 at 07:05
@SachinPasalkar OP doesn't asked to learn `Java`. I think you are overrated your self. No one here became genius by birth, you should learn to respect all who got higher as well as lower reputation people than you — Ruchira Gayan Ranaweera, Dec 12 '13 at 07:07
@user755806 look at my edit. now only EmpRequest implements equals. — kai, Dec 12 '13 at 07:13

score 2 · Answer 1 · answered Dec 12 '13 at 06:55

2

you can just generate equals() and hashCode() from IDE (Eclipse, IntelliJ IDEA) . That will enough for your scenario.

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Result)) return false;

    Result result = (Result) o;

    if (hid != null ? !hid.equals(result.hid) : result.hid != null) return false;
    if (id != null ? !id.equals(result.id) : result.id != null) return false;
    if (name != null ? !name.equals(result.name) : result.name != null) return false;

    return true;
}

@Override
public int hashCode() {
    int result = id != null ? id.hashCode() : 0;
    result = 31 * result + (name != null ? name.hashCode() : 0);
    result = 31 * result + (hid != null ? hid.hashCode() : 0);
    return result;
}

answered Dec 12 '13 at 06:55

Ruchira Gayan Ranaweera

34,993
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Ruchira, i need to write it based on Request object properties in EmpRequest. – user755806 Dec 12 '13 at 07:06
`equals()` and `hashCode()` are the properties which related to object it self. you have to implement those inside that object. Not any where else. – Ruchira Gayan Ranaweera Dec 12 '13 at 07:12
@user755806 when we doing a coding it is a good practice to implement `equals()` and `hashCode()`. That's depends on IDE warning level actually. – Ruchira Gayan Ranaweera Dec 12 '13 at 07:14
Ruchira, do i need to generate hashcode based on the properties of Request class? Thanks! – user755806 Dec 12 '13 at 07:15
@user755806 If you want to consider about Request class, yes it is. – Ruchira Gayan Ranaweera Dec 12 '13 at 07:18

kai · Accepted Answer · 2013-12-12T07:12:50.457

0

Edit:

public class Request implements Serializable{

     private String id;
     private String name;
     private String hid;

        public String getId()
        {
            return id;
        }

        public String getName()
        {
            return name;
        }

        public String getHid()
        {
            return hid;
        }
}

    public class EmpRequest implements Serializable{
         private Request request;

        public Request getRequest()
        {
            return request;
        }

         @Override 
         public boolean equals(Object obj) {
             if(obj==null)
                 return false;
             if(((EmpRequest) obj).getRequest().getId().equals(this.getRequest().getId()))
                 return true;
             else if(((EmpRequest) obj).getRequest().getName().equals(this.getRequest().getName())
                     &&((EmpRequest) obj).getRequest().getHid().equals(this.getRequest().getHid())) {
                 return true;
             }
             else
                 return false;
         }
    }

Here is the hashcode too:

@Override
public int hashCode()
{
    final int prime = 31;
    int result = 1;
    result = prime * result + ((getRequest().getId() == null) ? 0 : getRequest().getId().hashCode());
    result = prime * result + ((getRequest().getName() == null) ? 0 : getRequest().getName().hashCode());
    result = prime * result + ((getRequest().getHid() == null) ? 0 : getRequest().getHid().hashCode());
    return result;
}

edited Dec 12 '13 at 07:12

answered Dec 12 '13 at 07:02

kai

6,702
22
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kai, i cannot implement equals() and hashCode() in my Request class.It is third party class. I have to do it in EmpRequest class. – user755806 Dec 12 '13 at 07:03
Request class is not my own class and i cannot modify it. It is provided by third party. Thanks! – user755806 Dec 12 '13 at 07:09
kai, thanks for your answer. i understood equals(). How can i write hashCode() in this case? do i need to generate hashcode based on the properties of Request class ? Thanks! – user755806 Dec 12 '13 at 07:14
kai, while generating the hashCode(), what if getRequest() itself is null? how to deal in null scenario? thanks! – user755806 Dec 12 '13 at 07:21
oh i forgot this scenario. You can add a if condition and if getRequest() is null, return 1. – kai Dec 12 '13 at 07:32
I'm sorry, but your `equals` **is not transitive** and is **incompatible with** the `hashCode`. I guess, the OP's requirements are impossible to satisfy, but your answer is nonetheless wrong. – maaartinus Jun 15 '14 at 17:43

overriding equals and hashcode methods in java?

Request.java

2 Answers2

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