CODEWITHSUNDEEP
javalistarraylist
pals
pals

Reputation: 5

How to set values in ArrayList

I'm creating an ArrayList of type B: 

ArrayList<B> cert= new ArrayList<B>;
B a  = util.getCerts(path).iterator().next();
this.cert.add(a);
this.certNode(certs);

I'm getting a null pointer exception when I try to set the value:

void certNode(ArrayList<B> certResp) 
{       
    ArrayList<RespNode> exp = new ArrayList<RespNode>();
    for (int i = 0; i< certResp.size(); i++) {  
        exp.get(i).setxxx(certResp.get(i).getxxx());
        exp.get(i).setxxx(certResp.get(i).getxxx().toString());     
    }
 }

Any help would be great!

Upvotes: 0

Views: 561

Answers (5)

Shoaib Chikate
Shoaib Chikate

Reputation: 8975

As you are creating new empty ArrayList i.e []

exp.get(i)

gives you null

Instead you can use add method of ArrayList

void certNode(ArrayList<B> certResp) {
    //Here new empty list is created i.e exp=[] //no elements inside
    //Suppose your certResp=[B@12312,B@123834] i.e two B class objects     
    ArrayList<RespNode> exp = new ArrayList<RespNode>();

    for (int i = 0; i< certResp.size(); i++) {  //Size of certResp=2 as it contains 2 B objects  
        RespNode res=new RespNode(); //Create a RespNode class as you want to add of certResp ArrayList<RespNode>

        res.setxxx(certResp.get(i)); //Take value of xxx method of certResp.get(i) i.e B object xxx method and set into res.setXXX or RespNode class

        exp.add(res); //add res object into ArrayList
    }
 }

Upvotes: 0

Eran
Eran

Reputation: 393781

Since you just created the ArrayList instance exp, exp.get(i) doesn't exist, so you can't call exp.get(i).setxxx(...).

EDIT :

Try :

void certNode(ArrayList<B> certResp) {      
    ArrayList<RespNode> exp = new ArrayList<RespNode>();
    for (int i = 0; i< certResp.size(); i++) {  
        exp.add(certResp.get(i).getxxx());     
    }
 }

It's hard to be sure without knowing the return value of certResp.get(i).getxxx(), but if it returns RespNode, the code above would add that RespNode instance of the list.

Upvotes: 2

Attila Nepar&#225;czki
Attila Nepar&#225;czki

Reputation: 476

    void certNode(ArrayList<B> certResp) {      
        ArrayList<RespNode> exp = new ArrayList<RespNode>();
        for (int i = 0; i< certResp.size(); i++) {  
            exp.add(new RespNode()); // <----- 
            exp.get(i).setxxx(certResp.get(i).getxxx());
            exp.get(i).setxxx(certResp.get(i).getxxx().toString());     
        }
     }

btw you can improve syntax

    void certNode(ArrayList<B> certResp) {      
        ArrayList<RespNode> exp = new ArrayList<RespNode>();
        for (B b : certResp){
          RespNode resp = new RespNode();
          resp.setxxxx(b.getxxxx());
          exp.add(resp);
        }
     }

Upvotes: 0

univise
univise

Reputation: 509

Your list 'exp' is empty. In the for-loop you get a value of null; calling a method from null will cause the NullPointerException.

You have to put values in the list before you try to access them.

Upvotes: 0

jchampemont
jchampemont

Reputation: 2773

The problem is here : exp.get(i). exp is the newly created ArayList, so it's empty, so there is a null at index i

Upvotes: 1

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