Why do I need to create an instance of the ArrayList explicitly in the Managed Bean here?

Question

Consider:

<h:body>
        <h:dataTable value="#{integerListEntriesBean.racePlacement}" var="placement">
            <h:column>
                <h:outputText value="#{placement}" />
            </h:column>
        </h:dataTable>
</h:body>

The ManagedBean:

public class IntegerListEntriesBean {

    // Notice carefully here just an object reference of type List<> exists
    private List<Integer> racePlacement;


    public List<Integer> getRacePlacement() {
        return racePlacement;
    }

    public void setRacePlacement(List<Integer> racePlacement) {
        this.racePlacement = racePlacement;
    }

}

Entry in the faces-config.xml:

    <managed-bean>
        <managed-bean-name>integerListEntriesBean</managed-bean-name>
        <managed-bean-class>com.jsf.ch5.IntegerListEntriesBean</managed-bean-class>
        <managed-bean-scope>request</managed-bean-scope>
        <managed-property>
            <property-name>racePlacement</property-name>
            <property-class>java.util.List</property-class>
            <list-entries>
                <value-class>java.lang.Integer</value-class>
                <value>30</value>
                <value>10</value>
                <value>50</value>
                <value>40</value>
                <value>20</value>
            </list-entries>
        </managed-property>
    </managed-bean>

O/P:

30 
10 
50 
40 
20

So, ofcourse something this happened internally: List racePlacement = new ArrayList();

Now, if i make a slight change in the ManagedBean so as to add elements to the ArrayList inside the contructor

public class IntegerListEntriesBean {
    // Notice carefully here I had to explicitly create an object here.
    private List<Integer> racePlacement = new ArrayList<Integer>();
    public IntegerListEntriesBean(){
        racePlacement.add(500);
        racePlacement.add(600);
    }

    public List<Integer> getRacePlacement() {
        return racePlacement;
    }

    public void setRacePlacement(List<Integer> racePlacement) {
        this.racePlacement = racePlacement;
    }

}

O/P now:

500 
600 
30 
10 
50 
40 
20 

Since the object (new ArrayList<>()) gets created internally(meaning manually not created by me), Why do I need to explicitly create the object in the ManagedBean now(in the second case)? i.e

List<Integer> racePlacement = new ArrayList<Integer>();

Answer 1

This is necessary because the constructor is executed before faces-config processor. racePlacement must be a object to support 'add' method.