public String getVpcId() {
        return this.vpcId;
    }
<p>
If <b>AllowsVpcAndNonVpcInstanceMemberships</b> is <code>false</code>, this field is blank. If
<b>AllowsVpcAndNonVpcInstanceMemberships</b> is <code>true</code> and this field is blank, then this option group
can be applied to both VPC and non-VPC instances. If this field contains a value, then this option group can only
be applied to instances that are in the VPC indicated by this field.
</p>

@return If <b>AllowsVpcAndNonVpcInstanceMemberships</b> is <code>false</code>, this field is blank. If
        <b>AllowsVpcAndNonVpcInstanceMemberships</b> is <code>true</code> and this field is blank, then this
        option group can be applied to both VPC and non-VPC instances. If this field contains a value, then this
        option group can only be applied to instances that are in the VPC indicated by this field.
aws-java-sdk-rds/src/main/java/com/amazonaws/services/rds/model/OptionGroup.java