Issue with Java HashMap Assignment

Question

For some reason this function in my project is failing:

public void SetPlayersLineups(HashMap<Integer, Player> _players, 
    ArrayList<Integer> _lineup, boolean isAwayTeam) {

    System.out.println(_players.get(2)); //works properly
    System.out.println(_players.get(2).getNumberHits()); //null pointer exception

    if (isAwayTeam) {
        this.awayLineup = _lineup;
        this.awayPlay = _players;
    } else {
        this.homeLineup = _lineup;
        this.homePlay = _players;
    }

}

/* from Player class */

public int getNumberHits() {

    return this.hits;

}

I have a Player class, with a member get function getNumberHits(). The this.awayPlay and this.homePlay properties are not being set correctly. So I debugged with the System.out.println statements. The first returns a Player instance correctly. But when I call the get function I get a null pointer exception. Any ideas?

Miquel · Accepted Answer · 2014-01-26 15:30:57Z

2

Ok, one thing at a time. First off, you're printing _players.get(2).getNumberHits() and getting a NPE. Either _players.get(2) returns null, or getNumberHits() does something that throws an NPE. What cannot be the case is that _players2 is null since you already said that worked.

So, you need to look into what's wrong with the object _players you are being passed. I would suggest you try setting a breakpoint and analysing the object with your IDE (e.g. Eclipse or Netbeans)

answered Jan 26, 2014 at 15:30

Miquel

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Bohemian · Accepted Answer · 2014-01-26 15:38:52Z

1

If hits is declared as an Integer and is null, this method:

Integer hits; // default value of objects is null

public int getNumberHits() {
    return hits;    
}

will throw an NPE due to auto unboxing, because the method actually compiles as:

public int getNumberHits() {
    return hits.intValue();    
}

Either assign a value to hits:

Integer hits = 0;

or give hits the type of int, whose default value is 0, not null:

int hits;

edited Jan 26, 2014 at 15:38

answered Jan 26, 2014 at 15:33

Bohemian♦

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1 Comment

The Hawk Over a year ago

I have hits assigned as an integer property declaration: private int hits = 0;

Jakub Kubrynski · Accepted Answer · 2014-01-26 15:33:10Z

0

The problem is that hits is null, and Java tries to autobox hits (which is Integer) to int, and produces NullPointerException

answered Jan 26, 2014 at 15:33

Jakub Kubrynski

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