i am unable to display a toast message modal in lightning application ,what is the reason?

Hi,

<aura:component implements="flexipage:availableForRecordHome,force:hasRecordId" access="global" >
    <div>
        <lightning:button label="Information"
                          variant="brand"
                          onclick="{!c.showInfoToast}"
                          >
        </lightning:button>
        <lightning:button label="Error"
                          variant="destructive"
                          onclick="{!c.showErrorToast}">
        </lightning:button>
        <lightning:button label="Warning"
                          variant="inverse"
                          onclick="{!c.showWarningToast}"
                          class="wk_warning">
        </lightning:button>
        <lightning:button label="Success"
                          variant="inverse"
                          onclick="{!c.showSuccessToast}"
                          class = "wk_success">
        </lightning:button>
    </div>
</aura:component>

for more you can take help from https://webkul.com/blog/forceshowtoast-in-lightning/