CODEWITHSUNDEEP
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aradhya
aradhya

Reputation: 49

how to set dynamic Date value to Map<String,Object>?

I would like to set dynamic Date values to the Map<String,Object> and display that in the UI. I am working on JSF2. Here is my code

private  Map<String, Object> selectDates;
    {
        selectDates = new LinkedHashMap<String, Object>();
        selectDates.put("First Date", "111"); //label, value
        selectDates.put("Second Date", "222");
    }
    public Map<String, Object> getSelectDates()
        {
            return selectDates;
        }

I am having a drop down with label "First Date" and "Second Date" , now i have to assign values to these key dynamically. It does not work if i give as below:

 private  Date exDate;
private Date frontDate;
private  Map<String, Object> selectDates;
    {
        selectDates = new LinkedHashMap<String, Object>();
        selectDates.put("First Date", exDate;); //label, value
        selectDates.put("Second Date", frontDate;);
    }

public Map<String, Object> getSelectDates() {
    return selectDates;
}

I tried using private Map<String, Date> selectDates; but this does not give me value, it gives me null.

Upvotes: 1

Views: 863

Answers (1)

alainlompo
alainlompo

Reputation: 4434

You are using a non - static initalization code block. This code will only be executed when an instance of the containing class is created. Here is what I've got when I am trying to use your code

public class DatesInHash {

     private  Date exDate;
     private Date frontDate;
     private  Map<String, Object> selectDates;
     {
         //exDate = new Date();
         selectDates = new LinkedHashMap<String, Object>();
         selectDates.put("First Date", exDate); //label, value
         selectDates.put("Second Date", frontDate);
     }

     public Map<String, Object> getSelectDates() {
         return selectDates;
     }

     public void doDemo() {
         exDate = new Date();
         frontDate = new Date();
         Map<String, Object> datesMap = getSelectDates();

         System.out.println(((Date)datesMap.get("First Date")).toString());

     }

     public static void main(String[] args) {
         DatesInHash dIH = new DatesInHash();
         dIH.doDemo();

     }

}

When I execute this application I get a null pointer exception because at the moment the object gets constructed the non - static block gets invoked and since your two Date variables are null, it triggers the exception.

However if I uncomment this line of code //exDate = new Date();, I will work fine and displays a formatted version of the date variable.

Unless you need to use a non - static iniatialization bloc for a very specific reason I suggest that you create a simple initialization method of your map such as 

 public void initMap() {

     selectDates = new LinkedHashMap<String, Object>();
     selectDates.put("First Date", exDate); //label, value
     selectDates.put("Second Date", frontDate);


 }

And it will only be called after you are sure that the two dates are well initialized. If using the non - static block is mandatory then you need to properly initialize your date objects first.

More usefull infos on the use of non static initialization code blocks here and here

Upvotes: 1

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