Better Default Objects

Over the past couple of weeks, IJDK has been expanded with some very cool behavior. A new interface, HasInstanceValues, can be implemented by subclases, and static methods in the class Objects can provide the implementation of equals, hashCode, and toString. Therefore, HasInstanceValues subclasses only need to delegate to the same methods in Objects.

For example, in the KeyValue class (edited for brevity),

    public boolean equals(Object obj) {
        if (obj instanceof KeyValue) {
            KeyValue<?, ?> other = (KeyValue)obj;
            return Objects.equals(this, other);
        }
        else {
            return false;
        }
    }

    public int hashCode() {
        return Objects.hashCode(this);
    }

    public String toString(String sep) {
        return Objects.toString(this);
    }

    public Array<Object> getInstanceValues() {
        return Array.of(key, value);
    }

Objects#equals simply compares each element returned by getInstanceValues:

    public static boolean equals(HasInstanceValues x, HasInstanceValues y) {
        if (x == null) {
            return y == null;
        }
        else if (y == null) {
            return false;
        }
        else {
            return Arrays.equals(getInstanceObjects(x), getInstanceObjects(y));
        }
    }

Similarly, hashCode and toString use the elements returned by getInstanceObjects:

    public static int hashCode(HasInstanceValues x) {
        return x == null ? 0 : Arrays.hashCode(getInstanceObjects(x));
    }

    public static String toString(HasInstanceValues x) {
        return toString(x, ", ");
    }

    public static String toString(HasInstanceValues x, String delim) {
        return x == null ? null : x.getInstanceValues().join(delim);
    }

This eliminates much of the boilerplate methods that are common to many classes.

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