从ArrayList获取随机元素，添加到另一个ArrayList并从第一个ArrayList Android中删除该元素

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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