How To view or update three objects records in one visualforce page through custom controller

Visualforce page code

<apex:page controller="threeobjects">
    <apex:pageBlock >
    <apex:form >
    <apex:inlineEditSupport />
        <apex:pageBlockSection columns="3" >
            <apex:pageBlockTable value="{!accountname}" var="a">
                <apex:column headerValue="Accounts" >
                <apex:outputField value="{!a.name}"/>
                </apex:column>
            </apex:pageBlockTable>
            <apex:pageBlockTable value="{!contactname}" var="c">
                <apex:column headerValue="Contacts" >
                <apex:outputField value="{!c.name}"/>
                </apex:column>
            </apex:pageBlockTable>
            <apex:pageBlockTable value="{!opportunityname}" var="o">
                <apex:column headerValue="Opportunities" >
                <apex:outputField value="{!o.name}"/>
                </apex:column>
            </apex:pageBlockTable>
        </apex:pageBlockSection>
  
        <apex:commandButton value="Save" action="{!save}"/>
        </apex:form>
    </apex:pageBlock>
</apex:page>




Controller

public class threeobjects {
    public list<account> accountname{get; set;}
    public list<contact> contactname{get;set;}
    public list<opportunity> opportunityname{get; set;}

    public threeobjects(){
        accountname = [select name from account limit 10];
        contactname = [select name from contact limit 10];
        opportunityname = [select name from opportunity limit 10];
    }
    public PageReference save() {
        update accountname;
        update contactname;
        update opportunityname;
        return null;
    }
}