Fixed Array Practice and Common Solutions

Fixed arrays are often used in many standard problems. We will examine the most common use.

First some data to work with:

  1. To define and initialize a fixed array A with 5 chars with A[0] = 't' and A[4] = 'm':

             private char[] A = { 't',           'p',      'd',          'a',        'm'    };
     

  2. To define and initialize a fixed array B with 5 Strings with B[0]="tomato" and B[4]="mango":

            private String[] B = {"tomato",  "pear",  "durian",  "apple",  "mango"};
     

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

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

 

A

B
Define
Initialize		 public class ExampleA
{
   private char[] A = { 't', 'p', 'd', 'a', 'm'  };
 

OR

public class ExampleA
{
   private char[] A ;

   public ExampleA()
   { 
       A = new char[5];

       A[0] = 't';
       A[1] = 'p';
       A[2] = 'd';
       A[3] = 'a';
       A[4] = 'm';
   }

public class ExampleB
{
   private String[] B = {"tomato", "pear", "durian",
                                 "apple", "mango" };

OR

public class ExampleB
{
   private String[] B;

   public ExampleB()
   { 
       B = new String[5];

       B[0] = "tomato";
       B[1] = "pear";
       B[2] = "durian";
       B[3] = "apple";
       B[4] = "mango";
   }

Print public void print( ) {

    for( int i=0; i < A.length; i++)

        System.out.println( A[ i ] );

}

public void print( ) {

    for( int i=0; i < B.length; i++)

        System.out.println( B[ i ] );

}

Find

Return
index
where s
found
or -1
if not

    public int find( char s ) {

      for (int i=0; i < A.length; i++)

         if( A[ i ] == s )

            return i;

      return -1;
   }

    public int find( String s ) {

      for (int i=0; i < B.length; i++)

         if( B[ i ].equals( s ) )

            return i;

      return -1;
   }
Minimum
 		 public char minimum() {

   char min = A[0];

   for (int i=0; i < A.length; i++)

        if( A[ i ] < min )

           min = A[ i ];

   return min;
}

 public String minimum() {

   String min = B[0];

   for (int i=0; i < B.length; i++)

        if( B[ i ].compareTo( min ) < 0 )

           min = B[ i ];

   return min;
}
Index
of
Minimum		 public int indexOfMinimum( ) {

   int index = 0;

   for (int i=0; i < A.length; i++)

       if( A[ i ] < A[ index ] )

          index = i;

   return index;
}

 public int indexOfMinimum( ) {

   int index = 0;

   for (int i=0; i < B.length; i++)

       if( B[ i ].compareTo( B[ index ] ) < 0 )

          index = i;

   return index;
}
Total

 

 public String total( ) {

   String result = "";

   for (int i=0; i < A.length; i++)

       result = result + A[ i ];

   return result;
}

 public String total( ) {

   String result = "";

   for (int i=0; i < B.length; i++)

       result = result + B[ i ];

   return result;
}
Maximum
at
End		 public void maximumAtEnd() {

      for(int j=0; j < A.length - 1; j++)

         if( A[ j ] > A[ j+1 ] )
         {
               char temp=A[ j ];

               A[ j ]=A[ j+1 ];

               A[ j+1 ]=temp;

         }
}

 public void maximumAtEnd()  {

      for(int j=0; j < B.length - 1; j++)

         if( B[ j ].compareTo( B[ j+1 ] ) > 0 )
         {
               String temp=B[ j ];

               B[ j ] = B[ j+1 ];

               B[ j+1 ] = temp;

         }
}
Sort
 		 public void sort() {

   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;

         }
}

 public void sort()  {

   for(int pass=1; pass < B.length; pass++)

      for(int j=0; j < B.length-pass; j++)

         if( B[ j ].compareTo( B[ j+1 ] ) > 0 )
         {
               String temp=B[ j ];

               B[ j ] = B[ j+1 ];

               B[ j+1 ] = temp;

         }
}

Practice - Work in Pairs

  1. The instructor should provide candy and 5 cups.

    Label each Cup 0, 1, 2, 3 and temp.

    Put obviously different volumes of candy in Cup 0-3.

    Arrange Cup array in numerical order: 0, 1, 2, 3

     

  2. Hand execute the following algorithm using your real Candy cup array.

    Always keep the the cups in 0-3 order.

    Follow the algorithm, pouring cup contents.
     

    for( int j=0; j < cup.length - 1; j++)

             if( cup[ j ] > cup[ j+1 ] )
             {
                   Candy temp=cup[ j ];

                   cup[ j ]=cup[ j+1 ];

                   cup[ j+1 ]=temp;

             }

     

  3. Continue with the cup array from above. Hand execute the sort algorithm below.

    public void sort() {

       for(int pass=1; pass < cup.length; pass++)

          for(int j=0; j < cup.length - pass; j++)

             if( cup[ j ] > cup[ j+1 ] )
             {
                   Candy temp=cup[ j ];

                   cup[ j ]=cup[ j+1 ];

                   cup[ j+1 ]=temp;

             }
    }
    • Write the value of pass and j.
    •      pass                 j      
              1

       

       

       

       

       

       

       

      		        0

      Follow the algorithm, pouring cup contents.

      Always keep the the cups in 0-3 order.
       

    • When finished the candy should be sorted by volume.
       
    • Now eat some candy.
  4. Let's look at Candy sorting more closely.

    We assumed Candy class and cup fixed array existed.

    Also that if( cup[ j ] > cup[ j+1 ] ) worked.

    What are the actual definitions required?

    public class Candy {

          private int volume;

          public Candy( int volume )
          {
                 this.volume = volume;
          }

          public int getVolume()
          {
                 return volume;
          }
    }

     

     


     40          80         20        60         

    		public class CandyLand {

       Candy cup[ ] = { new Candy( 40 ) ,

                               new Candy( 80 ),

                               new Candy( 20 ),

                               new Candy( 60 )
                             };

      public void sort() {

        for(int pass=1; pass < cup.length; pass++)

          for(int j=0; j < cup.length - pass; j++)

             if( cup[ j ].getVolume() > cup[ j+1 ].getVolume() )
             {
                   Candy temp=cup[ j ];

                   cup[ j ]=cup[ j+1 ];

                   cup[ j+1 ]=temp;

             }
      }
    }

     

    Hand execute the sort while redrawing the object diagram.

     

     

  5. Write a CandyLand method to print all the Candy volumes of cup.
     
  6. Write a CandyLand method to total all the Candy volumes of cup.
     40          80         20        60  
        
  7. Write a CandyLand method to print all the Candy volumes of cup.
     
  8. Write a CandyLand method to return the greatest of the Candy volumes of cup.
     
  9. Hand sort fixed array A:

    char[] A = { 't', 'p', 'd', 'a', 'm'  };

    using the sort() method by completing the following table:
     
    pass j A[ j ] A[ j+1 ] temp A='t', 'p', 'd', 'a', 'm'
    1 0 't' 'p'    


     

  10. Hand sort fixed array B:

    String [] B = {"tomato", "pear", "durian", "apple", "mango"};

    using the sort() method by completing the following table:
     
    pass j B[ j ] B[ j+1 ] temp B="tomato", "pear", "durian", "apple", "mango"
    1 0 "tomato" "pear"    


     

    11.  

    Given the definitions below, give the Java to:

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

    String names[] = { "Brad", "C. G.", "Michael", "Joe", "Kyle" };

     

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

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

  12. 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;

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

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

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

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

  15. 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++;

  16. total the variables of list array.

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

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

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

     

  18. 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 ] );

     

  19. print the value of the variable in the middle of array names using the size() of names.

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

     

  20. reverse the values so that list[0] is 4, list[1] is -18, etc. Hint: while may be simpler than a for statement.

    int l = 0;
    int r = list.length-1;
    int temp;

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

     

  21. reverse the values so that names[0] is "Kyle", names[1] is "Joe", 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;
    }