I would like to know how to delete a randomly selected item from an arraylist and add that selected item to another empty arraylist.
An Additonal (Optional): I would like to also know how to compare elements in an ArrayList with another ArrayList. This one is a pain in my patuski.
well to move an element from one ArrayList to the other you can do something like this:
ArrayList< SomeClass > firstList;
ArrayList< SomeClass > secondList;
int randomlySelectedIndex; //initialize this to be random
SomeClass element = firstList.get( randomlySelectedIndex );
firstList.remove( randomlySelectedIndex );
secondList.add( randomlySelectedIndex );
As for comparing elements from 2 lists, you could make a compare method like so:
int compare( SomeClass first, SomeClass second ) {
//return 0, 1 or -1 depending on your criteria of how first relates to second
}
and then use the compare method when iterating through both lists
int result;
for( int x = 0; x < firstList.size(); x++ ) {
for( int y = 0; y < secondList.size(); y++ ) {
result = compare( firstList.get( x ), secondList.get( y ) );
if( result == 0 ) {
//do stuff
}
else if( result < 0 ) {
//do stuff
}
else {
//do stuff
}
}
}
please note that you should not be adding or removing elements from either of the arraylists from inside the 2 for loops unless you know the consequences of doing so.
Something like this should do the trick
List<T> list;
List<T> emptyList;
...
Random rand = new Random();
int randomIndex = rand.getInt() % list.size();
T item = list.remove(randomIndex);
emptyList.add(item);
As far a comparing two lists, you should clarify what exactly you want to compare. Also, since the two questions are fairly different, you may want to ask it in a separate post.
You can remove object from the ArrayList by calling remove(int index) which returns the object that was removed. Then you add that object to the other ArrayList with add():
SomeObject removedObject = firstList.remove(randomNum);
secondList.add(removedObject);
Note: make sure that random number is from 0 to the size of your ArrayList.
You can compare objects of the same class by implementing Comparable interface in that class. See more: https://docs.oracle.com/javase/tutorial/collections/interfaces/order.html
