Correct way to extend a class so I can override equals()

I have a class in a package that I cannot alter. This class does not override Object.equals() and having a different implementation of equals would really make my code cleaner.

I know I can't do this:

MyClass extends OtherClass{
@Override
public boolean equals(MyClass that)
{
//compare members and other stuff here
}
}

OtherClass oc1 = new OtherClass();
Other开发者_如何学GoClass oc2 = new OtherClass();
oc1.equals(oc2); //false because of Object.equals
//I want to do something like the following
MyClass mc1 = (MyClass) oc1; //throws class cast exception
MyClass mc2 = (MyClass) oc2; //throws class cast exception
mc1.equals(mc2); //true

What is the right way to accomplish this?

I could write a method like equals(OtherClass oc1, OtherClass oc2) but this is less useful. If I can implement equals I can make use of things like List.contains or Sets to manage my data and make life easier.

How about creating a wrapper class?

MyWrapper {
    private OtherClass data;

    MyWrapper(OtherClass data) {
        this.data = data;
    }

    public boolean equals(Object that) {
        ...
    }
}

Add getter for stored object, if necessary.

Do not override equals and not override hashCode. Also, embrace Apache Commons lang, it provides many useful classes. Using the Apache Commons EqualsBuilder and the Apache Commons HashCodeBuilder classes Your class-that-provides-the-missing-equals-operation will look something like this:

public class NiceBerry extends NaughtyBerry
{
    public boolean equals(Object rhsObject)
    {
        if (rhsObject == null)
        {
            return false;
        }

        if (rhsObject == this)
        {
            return true;
        }

        if (rhsObject instanceof NiceBerry)
        {
            EqualsBuilder equalsBuilder = new EqualsBuilder();
            NiceBerry rhs = (NiceBerry)rhsObject;

            equalsBuilder.append(getField1(), rhs.getField1());
            equalsBuilder.append(getField2(), rhs.getField2());
            ... append all the naughty berry fields

            return equalsBuilder.isEquals();
        }
        else
        {
            return false;
        }
    }

    public int hashCode()
    {
        // you pick a hard-coded, randomly chosen, non-zero, odd number
        // ideally different for each class
        HashCodeBuilder hashBuilder = new HashCodeBuilder(17, 37);

        hashBuilder.append(getField1());
        hashBuilder.append(getField2());
        ... append all the naughty berry fields

        return hashBuilder.toHashCode();
    }
}

I googled and found this: example