Question

In this exercise, you will create a couple of helper methods for ArrayLists in a class called ArrayListMethods.

Answer 1

Answer:

package lab1;

import java.util.ArrayList;

import java.util.Iterator;

public class ArrayListMethodsTester

{

public static void main(String[] args)

{

ArrayList<String> stringArray = new ArrayList<String>();

stringArray.add("This");

stringArray.add("is");

stringArray.add("an");

stringArray.add("ArrayList");

stringArray.add("of");

stringArray.add("Strings");

System.out.println("Printing the arraylist:");

ArrayListMethods.print(stringArray);

System.out.println("\nArrayList is condensing:");

ArrayListMethods.condense(stringArray);

ArrayListMethods.print(stringArray);

System.out.println("\nArrayList is duplicating:");

ArrayListMethods.duplicate(stringArray);

ArrayListMethods.print(stringArray);

}

}

class ArrayListMethods

{

static void print(ArrayList stringArray)

{

  Iterator it = stringArray.iterator();

  while (it.hasNext())

     System.out.println(it.next() + " ");

     

}

static void condense(ArrayList stringArray)

{

  int length=stringArray.size();

     

  ArrayList cloneArray=(ArrayList) stringArray.clone();

     

  stringArray.clear();

  StringBuilder sb=new StringBuilder("");

     

  for (int i = 0; i < (length/2); i++)

  {

      sb.append(cloneArray.get(i));

      sb.append(" ");    

  }

  stringArray.add(sb);

     

  StringBuilder sb1=new StringBuilder("");

  for (int i = (length/2); i < length; i++)

  {

      sb1.append(cloneArray.get(i));

      sb1.append(" ");    

  }

  stringArray.add(sb1);

  }

static void duplicate(ArrayList stringArray)

{

  for (int i = 0; i < stringArray.size(); i+=2)

  {

      stringArray.add(i+1,stringArray.get(i));

  }

}

}

Explanation:

• Get the length of the arraylist  to copy the array into another arraylist .
• Empty the array so that new content can be stored in it .
• Use a loop to half of array_list.
• Use a loop from half of array_list to the end of arraylist and  append all into a single string.