How to iterate through an ArrayList of Objects of ArrayList of Objects?

Question

Using an example:

Let say I have a class call Gun. I have another class call Bullet.

Class Gun has an ArrayList of Bullet.

To iterate through the Arraylist of Gun ..instead of doing this:

ArrayList<Gun> gunList = new ArrayList<Gun>();
for (int x=0; x<gunList.size(); x++)
    System.out.println(gunList.get(x));

We can simply iterate through the ArrayList of Gun as such:

for (Gun g: gunList) System.out.println(g);

Now, I want to iterate and print out all Bullet of my 3rd Gun object:

for (int x=0; x<gunList.get(2).getBullet().size(); x++)  //getBullet is just an accessor method to return the arrayList of Bullet 
    System.out.println(gunList.get(2).getBullet().get(x));

Now my question is: Instead of using the conventional for-loop, how do I printout the list of gun objects using the ArrayList iteration ?

Why do you think there's a difference between your too case? As long as your class implements Iterable (and we know that List does) you can use a for-each loop. — PM 77-1
– PM 77-1, Commented Jul 24, 2014 at 20:53
For whom down voted this question, care to drop a reason here? I have checked through SO and no one asked this before. I hope you can justify your reason for down voting me. Thanks. — user3437460
– user3437460, Commented Jul 25, 2014 at 9:31
For any kind souls out there, if you think my question is alright, kindly give me an up vote to reverse this unjustified down vote. Thank you. — user3437460
– user3437460, Commented Jul 25, 2014 at 9:41

unholysampler · Accepted Answer · 2014-07-24 20:51:21Z

47

You want to follow the same pattern as before:

for (Type curInstance: CollectionOf<Type>) {
  // use currInstance
}

In this case it would be:

for (Bullet bullet : gunList.get(2).getBullet()) {
   System.out.println(bullet);
}

answered Jul 24, 2014 at 20:51

unholysampler

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1 Comment

user3437460 Over a year ago

You gave me exactly what I asked for. I tried it and it works. Thanks for everyone who contributed an answer.

0-4930-42390eo23o2e0-23oe0-23o · Accepted Answer · 2014-07-24 21:01:10Z

10

Edit:

Well, he edited his post.

If an Object inherits Iterable, you are given the ability to use the for-each loop as such:

for(Object object : objectListVar) {
     //code here
}

So in your case, if you wanted to update your Guns and their Bullets:

for(Gun g : guns) {
     //invoke any methods of each gun
     ArrayList<Bullet> bullets = g.getBullets()
     for(Bullet b : bullets) {
          System.out.println("X: " + b.getX() + ", Y: " + b.getY());
          //update, check for collisions, etc
     }
}

First get your third Gun object:

Gun g = gunList.get(2);

Then iterate over the third gun's bullets:

ArrayList<Bullet> bullets = g.getBullets();

for(Bullet b : bullets) {
     //necessary code here
}

edited Jul 24, 2014 at 21:01

answered Jul 24, 2014 at 20:55

0-4930-42390eo23o2e0-23oe0-23o

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Comments

Ray A · Accepted Answer · 2014-07-24 21:05:59Z

6

When using Java8 it would be more easier and a single liner only.

    gunList.get(2).getBullets().forEach(n -> System.out.println(n));

answered Jul 24, 2014 at 21:05

Ray A

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1 Comment

MC Emperor Over a year ago

Or even gunList.get(2).getBullets().forEach(System.out::println);.

Tsotne Tabidze · Accepted Answer · 2014-07-24 20:51:13Z

3

for (Bullet bullet : gunList.get(2).getBullet()) System.out.println(bullet);

answered Jul 24, 2014 at 20:51

Tsotne Tabidze

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1 Comment

Tsotne Tabidze Over a year ago

Seriously? I thought one line of a code usually doesn't need an explanation. Especially when the person who asked the question himself/herself wrote: "for (Gun g: gunList) System.out.println(g);"

Thorn · Accepted Answer · 2014-07-24 20:55:42Z

2

We can do a nested loop to visit all the elements of elements in your list:

 for (Gun g: gunList) {
   System.out.print(g.toString() + "\n   "); 
   for(Bullet b : g.getBullet() {
      System.out.print(g);    
   }
   System.out.println(); 
 }

answered Jul 24, 2014 at 20:55

Thorn

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Comments

Andrew Orobator · Accepted Answer · 2014-07-24 20:59:53Z

1

int i = 0; // Counter used to determine when you're at the 3rd gun
for (Gun g : gunList) { // For each gun in your list
    System.out.println(g); // Print out the gun
    if (i == 2) { // If you're at the third gun
        ArrayList<Bullet> bullets = g.getBullet(); // Get the list of bullets in the gun
        for (Bullet b : bullets) { // Then print every bullet
            System.out.println(b);
        }
    i++; // Don't forget to increment your counter so you know you're at the next gun
}

answered Jul 24, 2014 at 20:59

Andrew Orobator

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