overriding equals and hashcode methods in java?

问题

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?

回答1:

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;
}

回答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;
}

来源：https://stackoverflow.com/questions/20536890/overriding-equals-and-hashcode-methods-in-java

标签

java

hashcode

java-ee-7