Chapter 4 and 5 - Array and ArrayList comparison examples

The following are similar solutions using array and ArrayList objects. Three points of note:

  1. To define and initialize an array A with 5 chars with A[0]='l' and A[4]='o':

             private char[] A = { 'l',           'p',      'd',          'a',        'o'    };
     

  2. To define and initialize an array B with 5 Strings with B[0]="lychee" and B[4]="orange":

            private String[] B = {"lychee",  "pear",  "durian",  "apple",  "orange"};
     

  3. To compare two strings, essentially "apple" < "orange", the following prints the smaller of the two:

           if( "apple".compareTo("orange") < 0)
               System.out.println("apple");
           else
               System.out.println("orange");
     

Define

Array

public class arrayExample
{
  private char[] A =
    { 'l',     'p',    'd',      'a',      'o'  };

   private String[] B =
                                  {"lychee",
                                    "pear",
                                    "durian",
                                    "apple",
                                    "orange"};

   public arrayExample()
   {  }

ArrayList

import java.util.ArrayList;

public class arrayListExample
 {
   ArrayList B = new ArrayList();

   public arrayListExample()
   {
      B.add("lychee");
      B.add("pear");
      B.add("durian");
      B.add("apple");
      B.add("orange");
   }
Print    public void printArray()
   {
      for (int i=0; i<B.length; i++)
          System.out.print(" " + B[ i ]);
   } 		   public void printArrayList()
   {
      for (int i=0; i<B.size(); i++)
           System.out.println( B.get( i ) );
   }
String
Search

Return
index
where s
found
or -1
if not

    public int searchString(String s)
   {
      for (int i=0; i<B.length; i++)
         if(((String)B[ i ]).equals( s ) )
            return i;
      return -1;
   }		    public int searchString(String s)
   {
      for (int i=0; i<B.size(); i++)
         if(((String)B.get( i )).equals( s ) )
            return i;
      return -1;
   }
Return
Least
char
 		 public char leastChar()
{
   char least = A[0];
   for (int i=0; i<A.length; i++)
        if(A[ i ] < least )
           least = A[ i ];
   return least;
}		   

   ArrayList is a collection of objects,

   no primitives such as char, int, boolean

Least
String		 public String leastString()
{
   String least = B[0];
   for (int i=0; i<B.length; i++)
       if(B[ i ].compareTo(least) < 0 )
           least = B[ i ];
   return least;
}		 public String leastString()
{
   String least = (String)B.get(0);
   for (int i=0; i<B.size(); i++)
       if(((String)B.get(i)).compareTo(least) < 0 )
            least = (String)B.get( i );
   return least;
}
Index
of
least
String		 public int indexOfleastString()
{
   int least = 0;
   for (int i=0; i<B.length; i++)
       if(B[ i ].compareTo(B[ least ]) < 0 )
          least = i;
   return least;
}		 public int indexOfleastString()
{
   int least = 0;
   for (int i=0; i<B.size(); i++)
     if(((String)B.get( i )).compareTo((String)B.get( least )) < 0 )
            least = i;
   return least;
}
Sort
char
array
ascending
 		 public char[] bubbleSort()
{
   for(int pass=1; pass < A.length; pass++)
      for(int j=0; j < A.length-pass; j++)
         if(A[ j ] > A[ j+1 ])
         {
               char temp=A[ j ];
               A[ j ]=A[ j+1 ];
               A[ j+1 ]=temp;
         }
   return A;
}		  

   ArrayList is a collection of objects,

   no primitives such as char, int, boolean

 
Sort
String
descending		 public String[] bubbleSort()
{
   for(int pass=1; pass < B.length; pass++)
      for(int i=0; i < B.length-pass; i++)
         if(B[ i ].compareTo(B[ i+1 ]) > 0)
         {
               String temp=B[ i ];
               B[ i ] = B[ i+1 ];
               B[ i+1 ] = temp;
         }
  return B;
}		 public ArrayList bubbleSort()
{
   for(int pass=1; pass < B.size(); pass++)
     for(int j=0; j<B.size()-pass; j++)
        if(((String)B.get(j)).compareTo((String)B.get(j+1)) < 0)
        {
               String temp=(String)B.get( j );
               B.set( j, B.get( j+1 ));
               B.set( j+1 , temp );
         }
   return B;
}

Practice

Given the definitions, give the Java to:

int list[] = { -4, -3, -6, -1, -7, -20, 15, -2, 27, -14, -18, 4, -5 };

String names[] = { "Josh", "Michelle", "Michael", "Tom", "Jason" };

  1. set all the variables of list array to 0.

    for(int i=0; i<list.length; i++) list[i] = 0;

  2. set all the variables of list array to a random number between -10 and 10.

    Random rN = new Random();
    for(int i=0; i<list.length; i++) list[i] = rN.nextInt(21)-10;

  3. set all the variables of names array to null.

    for(int i=0; i<names.length; i++) names[i] = null;

  4. set a random variable (0 to 4) of names array to "George".

    Random rN = new Random();
    names[ rN.nextInt(5) ] = "George";

  5. count the number of variables of list array less than 0.

    int count = 0:
    for(int i=0; i<list.length; i++)
       if( list[i] < 0 )
           count++;

  6. total the variables of list array.

    int total;
    for(int i=0; i<list.length; i++)
          total = total + list[ i ];

  7. concatenate the variable of names array into a single String.

    String single = "";
    for(int i=0; i<names.length; i++)
        single = single + names[ i ];

  8. print the value of the variable in the middle of array list using the length of list.

    int middle = list.length / 2;
    System.out.println( list[ middle ] );

  9. print the value of the variable in the middle of array names using the length of names.

    int middle = names.length / 2;
    System.out.println( names[ middle ] );

  10. reverse the list order so that list[0] is -5, list[1] is 4, etc. Hint: while may be simpler than a for statement.

    int b = 0;                  // beginning array index
    int e = list.length-1;   // end array index
    int temp;

    while( b < e )
    {
        temp = list[ b ];
        list[ b ] = list[ e ];
        list[ e ] = temp;
        b = b + 1;
        e = e - 1;
    }

  11. reverse the values so that names[0] is "Jason", names[1] is "Tom", etc.

    int l = 0;
    int r = names.length-1;
    String temp;

    while( l < r )
    {
        temp = list[ l ];
        list[ l ] = list[ r ];
        list[ r ] = temp;
        l = l + 1;
        r = r - 1;
    }