Adding values in List<String> dynamically

Question

Every time a new String is generated but the List is having null value for it.

<h:dataTable value="#{add.periods}" var="prd">
        <h:column><h:inputText value="#{prd}"  /></h:column>
    </h:dataTable>
    <h:commandButton value="add" action="#{add.addList}" />
    <h:commandButton value="submit" action="#{add.submit}" />
</h:dataTable>

Entity AddPeriods: object add

private List<String> periods = new ArrayList<String>();
    @ElementCollection
     public List<String> getPeriods() 
     {         
            return periods;
     }
        public void setPeriods(List<String> periods)      
        {

         this.periods=periods;
         }

         public void addList() 
         { 

          periods.add(new String());

         }
          public void submit()
          {
          System.out.println("periods..................................: " +periods);
           }

Message on Console:After 2 times addition

    periods..................................: [, ]

Jon Skeet · Accepted Answer · 2011-08-12 08:23:50Z

3

It's not adding a null value (it's not a null reference) - but it's not adding a useful value:

periods.add(new String());

In what way were you expecting that to be useful? Shouldn't you be adding a useful string value instead of just a new empty string?

answered Aug 12, 2011 at 8:23

Jon Skeet

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12 Comments

kanika Over a year ago

I am just entering a string like abc.One more thing whenever I click add Button the value added previously become null I mean the textbox becomes empty.

Jon Skeet Over a year ago

@kanika: But you're not adding that string into the list - you're just adding a new empty string. How did you expect that to work? It's not at all clear what frameworks you're using or how you're expecting any user data to make it into your class. I suspect this question is really very specific to the UI framework you're using, and you should read the tutorials for that framework. As you haven't even told us what framework it is, there's not a lot more we can do to help you.

kanika Over a year ago

"addList()" is doing addition of a String into the List for me. What I want is that when user click add button she/he can assign it a value.By the way i am working on "Spring web flow" framework.I also tried following code:private List<Item> items = new ArrayList<Item>(); public void add() { items.add(new Item()); } public void submit() { System.out.println("items: " + items); } @ElementCollection public List<Item> getItems() { return items; } public void setItems(List<String> Items) { this.items=items; } and it workswell

Jon Skeet Over a year ago

@kanika: You need to look at Spring Web Flow tutorials, basically - I can't tell from the code you've provided where the UI data is meant to get into your code.

kanika Over a year ago

from this UIData it is getting store into a List also in Db<h:form> <h:dataTable value="#{add.items}" var="item"> <h:column><h:inputText value="#{item.value}" /></h:column> </h:dataTable> <h:commandButton value="add" action="#{add.add}" /> <h:commandButton value="submit" action="#{add.submit}" /> <h:commandButton value="sub" action="submit" /> </h:form> I am trying to do the same thing with String type objects.

|

Andreas Johansson · Accepted Answer · 2011-08-12 08:27:08Z

2

You just add a new empty string. Switch it to something else, e.g:

periods.add(new String("hey there!"));

answered Aug 12, 2011 at 8:27

Andreas Johansson

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3 Comments

kanika Over a year ago

I want a new String to be added by the user.Here "hey there" will be a pre-defined one.One more thing when I write <h:column><h:inputText value="#{add.periods[0]}" /></h:column>,my value gets stored at index zero,Message at console becomes: periods..................................: [//value entered in textbox, ]

Jon Skeet Over a year ago

Why would you want to call the string constructor with a literal in this case? ;)

kanika Over a year ago

I tried ur code it results periods..................................: [hey there!,hey there!,hey there! ] ,but i want the value to be user defined.It is not accepting my changes.Please clarify my point whenever i press "add" button "addList()" get called which returns a String type object right.Now what I want is that a user can assign a value to it.Then it will get stored into a List.Why in this case I am not able to reassign a value to "hey there!" string.

Logan · Accepted Answer · 2011-08-12 11:37:32Z

1

Pass some String to the function addList, else it will keep on adding empty Strings to the list. When you write something like, periods.add(new String("Kanika")), and its added in List as many times as you press add button, that means your function is working fine. But unless and until you will pass something to it, it will not insert anything meaningful.

answered Aug 12, 2011 at 11:37

Logan

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2 Comments

kanika Over a year ago

but sir it will be a value defined by me i want it to be user-defined

Logan Over a year ago

That's what I meant when I said Pass Some String to the Function. Currently you are calling it like add.addList i.e with no parameters. Check the way of passing the parameter using the framework you are working with. and then use the corresponding syntax.

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