Java, Exception in thread "main" java.lang.NullPointerException caused due to not initializing an object

Question

Help me with this, "Exception in thread "main" java.lang.NullPointerException" thanks

private List< PosibleTerreno> posibles_terrenos;
private List< PosibleTerreno> terrenos_validos;

//-------------------------------

 int cantidad = this.posibles_terrenos.size(); 

        for (int i = 0 ; i < cantidad ; i++)
        {
            if(this.posibles_terrenos.get(i).get_validez() == true)
            {
                this.terrenos_validos.add(this.posibles_terrenos.get(i));
            }
        }

Make sure you have posibles_terrenos = new ... and same for terrenos_validos somewhere before executing the line throwing exceptiion — Karthik Kalyanasundaram
– Karthik Kalyanasundaram, Commented Mar 2, 2014 at 3:31
And then look at the exception message and stack trace, which will tell you exactly which line of which file it occurred on and what you were doing at the time. — keshlam
– keshlam, Commented Mar 2, 2014 at 3:31
You have to make sure posibles_terrenos and terrenos_validos are correctly initialized. — Ale Zalazar
– Ale Zalazar, Commented Mar 2, 2014 at 3:33
private List< PosibleTerreno> posibles_terrenos; private List< PosibleTerreno> terrenos_validos; it's defined next to " public class Controlador { " — Cardona Jeison
– Cardona Jeison, Commented Mar 2, 2014 at 3:33

Community · Accepted Answer · 2020-06-20 09:12:55Z

5

You have declared these variables

private List< PosibleTerreno> posibles_terrenos;
private List< PosibleTerreno> terrenos_validos;

but you have not initialized them. You need to do something along the lines of

private List< PosibleTerreno> posibles_terrenos = new ArrayList<PosibleTerreno>();
private List< PosibleTerreno> terrenos_validos = new ArrayList<PosibleTerreno>();

Otherwise, both lists are null, and attempting to reference any of their functions...doesn't even make sense, because there's no "their" there. They're nothing. So attempting this

int cantidad = this.posibles_terrenos.size();

will obviously result in a NullPointerException.

(+1 for three homophones in a row.)

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Mar 2, 2014 at 3:35

aliteralmind

20.2k17 gold badges80 silver badges109 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Community · Accepted Answer · 2017-05-23 12:03:41Z

3

You need to initialize your List(s), you might use a ArrayList and/or a LinkedList perhaps with -

private List<PosibleTerreno> posibles_terrenos = new ArrayList<PosibleTerreno>();
private List<PosibleTerreno> terrenos_validos = new LinkedList<PosibleTerreno>();

With Java 7 and above, you can also use the diamond operator like so -

private List<PosibleTerreno> posibles_terrenos = new ArrayList<>();
private List<PosibleTerreno> terrenos_validos = new LinkedList<>();

edited May 23, 2017 at 12:03

CommunityBot

11 silver badge

answered Mar 2, 2014 at 3:35

Elliott Frisch

202k20 gold badges166 silver badges265 bronze badges

Comments

tkt986 · Accepted Answer · 2014-03-02 03:35:04Z

2

do this before executing the line throwing the exception.

private List< PosibleTerreno> posibles_terrenos = new ArrayList<PosibleTerreno>();
private List< PosibleTerreno> terrenos_validos = new ArrayList<PosibleTerreno>();

answered Mar 2, 2014 at 3:35

tkt986

1,0264 gold badges17 silver badges25 bronze badges

Collectives™ on Stack Overflow

Java, Exception in thread "main" java.lang.NullPointerException caused due to not initializing an object

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related