Equals.java

public boolean equals(Object obj) {
    if (this == obj) {
        return true;
    }

    // Consider isAssignableFrom depending on actual needs.
    if (getClass() != obj.getClass()) {
        return false;
    }

    Pair other = (Pair) obj;

    if (left == null && other.left != null) {
        return false;
    }

    if (right == null && other.right != null) {
        return false;
    }

    return left.equals(other.left) && right.equals(other.right);
}