Array struct in java

Question

I am learning Java and I am doing some C++ codes into java, I am following this webpage http://uva.onlinejudge.org and trying to do some of the problems in Java. Now I am doing this problem http://uva.onlinejudge.org/index.phpoption=com_onlinejudge&Itemid=8&page=show_problem&problem=1072 and after researching and figure out how to do it on paper I found this webpage where the problems seems easy to follow: http://tausiq.wordpress.com/2010/04/26/uva-10131/

But now, and due to the fact I am new on Java, I want to learn how to do an array of struct in Java. I now I can do a class like a struct: if this is in C++

struct elephant {
    int weight;
    int iq;
    int index;
} a [1000 + 10];

I can do this in Java:

public class Elephant {
        private int _weight;
        private int _iq;
        private int _index;

        public Elephant(int weight, int iq, int index) {
            this._weight = weight;
            this._iq = iq;
            this._index = index;
        }

        public int getWeight() {
            return this._weight;
        }

        public int getIQ() {
            return this._iq;
        }

        public int getIndex() {
            return this._index;
        }

        public void setWeigth(int w) {
            this._weight = w;
        }

        public void setIQ(int iq) {
            this._iq = iq;
        }

        public void setIndex(int i) {
            this._iq = i;
        }
    }

But I don't know how I can turn this into the last part of the struct in c++:

a [1000 + 10];

I mean, having an array of a objects of the class Elephant in Java like having an array of elements elephants in c++

Could someone help me to understand it better..

Is there any point declaring the data members private in Java? They are public in your C++ example after all. — juanchopanza
– juanchopanza, Commented May 26, 2014 at 15:22

Chris Thompson · Accepted Answer · 2014-05-26 15:19:15Z

5

Arrays of objects in Java are accomplished the same way as an array of primitives. The syntax for this would be

Elephant[] elephants = new Elephant[1000+10];

This will initialize the array, but it will not initialize the elements. Any index into the array will return null until you do something like:

elephants[0] = new Elephant();

answered May 26, 2014 at 15:19

Chris Thompson

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3 Comments

neteot Over a year ago

Indeed, i was going to ask if i could do this: ArrayList<Elephant> elephant = new ArrayList<Elephant>(); thank you

Chris Thompson Over a year ago

@neteot you can! Although that's an ArrayList which is closer to an STL list or more generically a linked list. The ArrayList is another object that is backed by an array and allows you to dynamically adjust size etc. Arrays, once created, are a fixed size.

julaine Over a year ago

It will initialize the elements: with null, and that's a guaranteed behaviour. (This post is for C++-devs learning Java, so I think this pedantry is appropriate here, since C++ may do weirder things for an uninitialized array element)

Jens · Accepted Answer · 2014-05-26 15:19:11Z

1

This should be what you are loking for :

Elephant []  array = new Elephant[1010];

answered May 26, 2014 at 15:19

Jens

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2 Comments

neteot Over a year ago

Indeed, i was going to ask if i could do this: ArrayList<Elephant> elephant = new ArrayList<Elephant>(); thank you

Jens Over a year ago

@netot Yes you can do so.

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