Lecture on Arrays, 13 April 2004

Class Arrays

In the java.util package there is a class called Arrays that contains various methods for manipulating arrays. The methods that you will find useful are:

binarySearch ( array, key ) - searches the specified array for the key using the binary search algorithm.
equals ( array1, array2 ) - returns the boolean value true if array1 is equal to array2, otherwise it returns false.
fill ( array, value ) - fills the specified array with the specified value.
sort ( array ) - sorts the given array

I have appended a piece of code that shows how to use the methods in this class. Do not forget to use the import statement in your program.


import java.util.*;

public class TestArray
{
  // This method prints an array
  public static void printArray ( int[] anArray )
  {
    for ( int i = 0; i < anArray.length; i++ )
      System.out.print ( anArray[i] + "  " );
    System.out.println ();
  }

  public static void main ( String [] args )
  {
    // Create an array and print it
    int[] intArray = { 87, 23, 67, 46, 91, 52 };
    printArray ( intArray );

    // Sort the array and print it
    Arrays.sort ( intArray );
    printArray ( intArray );

    // Search for an item in the array
    int x = 46;
    int i = Arrays.binarySearch ( intArray, x );
    System.out.println ( "The number " + x + " is at " + i );

    // Search for an item not in the array
    x = 73;
    i = Arrays.binarySearch ( intArray, x );
    System.out.println ( "The number " + x + " is at " + i );

    // Create another array and test if they are equal
    int[] intArray2 = { 87, 67, 23, 46, 91, 52 };
    if ( Arrays.equals ( intArray, intArray2 ) )
      System.out.println ( "The arrays are equal.");
    else
      System.out.println ( "The arrays are not equal." );

    // Print the array, fill it with a specified value and print it
    // again to verify
    printArray ( intArray2 );
    Arrays.fill ( intArray2, -1 );
    printArray ( intArray2 );
  }
}