ArrayLists and Iterators
Read this chapter about lists and the useful methods that are available for adding and inserting elements into a list.
15. isEmpty()
Answer:
0: Amy
1: Bob
2: Deb
isEmpty()
isEmpty()
To check if an ArrayList
has elements use
boolean isEmpty()
which returns true
if the cells of the ArrayList
are all empty.
Warning:The value null
in a cell counts as data. An empty cell is not the same as a cell that contains null
.
To remove all elements from a list, use
void clear()
Question 15:
(Puzzle: ) What will the following program print?
import java.util.* ;
public class NullPuzzle
{
public static void main ( String[] args)
{
ArrayList<String> nobby = new ArrayList<String>();
System.out.println( "Case A:" + nobby.isEmpty() );
nobby.add( null );
System.out.println( "Case B:" + nobby.isEmpty() );
nobby.remove( 0 );
System.out.println( "Case C:" + nobby.isEmpty() );
nobby.add( "" );
System.out.println( "Case D:" + nobby.isEmpty() );
nobby.clear( );
System.out.println( "Case E:" + nobby.isEmpty() );
}
}