Iterating through two ArrayList with Nested While Statements - Java

Question

I am trying to iterate through two ArrayLists (called sceneObjects and animationSceneObjects) and match the two based on a name field. Here is my code :

Iterator<AnimationObject> itr = animationObjects.iterator();
Iterator<SceneObject> itrMain = sceneObjects.iterator();

while (itr.hasNext()) {
            AnimationObject object = itr.next();
            //Remove the word node from the animation object name so it matches main object name.
            String  tmpString = object.animationobjectName.replace("node-", "");
            System.out.println("Animation Object name is" +tmpString);
            while (itrMain.hasNext()) {
                SceneObject objectMain = itrMain.next();
                System.out.println("Scene Object name is" +objectMain.objectName);
                if (tmpString.equals(objectMain.objectName)) {
                    System.out.println("Animation Object matched to main object array" +tmpString);
                    objectMain.animations = object.animationData;
                    objectMain.hasAnimations = true;
                }
            }
        }

The problem is that the code isn't working as intended - it only compares the first item in the itr iterator to the values of the itrMain iterator.

Can anyone spot what I have got wrong ?

Thank you.

amit · Accepted Answer · 2012-05-10 12:31:04Z

You will have to reset itrMain before each run of the inner loop, otherwise - once you have exhausted the iterator the first time - the inner loop will never be invoked.

You can do it by re-assigning it with sceneObjects.iterator() before you reach the inner loop, or use an enhanced for-each loop

Iterator<AnimationObject> itr = animationObjects.iterator();

while (itr.hasNext()) {
            Iterator<SceneObject> itrMain = sceneObjects.iterator();
       //    ^
       //   reassigning itrMain each iteration of the outer loop

            AnimationObject object = itr.next();
            //Remove the word node from the animation object name so it matches main object name.
            String  tmpString = object.animationobjectName.replace("node-", "");
            System.out.println("Animation Object name is" +tmpString);
            while (itrMain.hasNext()) {
                SceneObject objectMain = itrMain.next();
                System.out.println("Scene Object name is" +objectMain.objectName);
                if (tmpString.equals(objectMain.objectName)) {
                    System.out.println("Animation Object matched to main object array" +tmpString);
                    objectMain.animations = object.animationData;
                    objectMain.hasAnimations = true;
                }
            }
        }

Matt Ball · Accepted Answer · 2012-05-10 12:26:05Z

Use a new iterator for the inner loop ever time:

Iterator<AnimationObject> itr = animationObjects.iterator();

while (itr.hasNext()) {
    AnimationObject object = itr.next();
    //Remove the word node from the animation object name so it matches main object name.
    String  tmpString = object.animationobjectName.replace("node-", "");
    System.out.println("Animation Object name is" +tmpString);

    Iterator<SceneObject> itrMain = sceneObjects.iterator();

    while (itrMain.hasNext()) {
        SceneObject objectMain = itrMain.next();
        System.out.println("Scene Object name is" +objectMain.objectName);
        if (tmpString.equals(objectMain.objectName)) {
            System.out.println("Animation Object matched to main object array" +tmpString);
            objectMain.animations = object.animationData;
            objectMain.hasAnimations = true;
        }
    }
}

or (perhaps more simply) use two for loops:

for (AnimationObject animation : animationObjects) {
    for (SceneObject scenes : sceneObjects) {
        // snip...
    }
}

Marko Topolnik · Accepted Answer · 2012-05-10 12:26:25Z

1

You're not restarting the inner iterator for every outer loop step. What you should really do is use the for-each loop.

for (AnimationObject ao : animationObjects) {
  ... your outer-loop code ...
  for (SceneObject so : sceneObjects) {
     ... your inner-loop code ...
  }
]

answered May 10, 2012 at 12:26

Marko Topolnik

201k31 gold badges336 silver badges455 bronze badges

Comments

Grims · Accepted Answer · 2012-05-10 12:26:37Z

1

You have to declare the itrMain iterator inside the first loop. If you keep the same iterator, your first iteration will have consumed it.

Iterator<AnimationObject> itr = animationObjects.iterator();
while (itr.hasNext()) {
    Iterator<SceneObject> itrMain = sceneObjects.iterator();
    [...]

answered May 10, 2012 at 12:26

Grims

8076 silver badges6 bronze badges

Collectives™ on Stack Overflow

Iterating through two ArrayList with Nested While Statements - Java

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related