range() in Java

tutego (Chrsitian Ullenboom) — Tue, 24 Apr 2007 13:20:16 GMT

A range is a very handy feature of programing languages like Python.

* range( 10 ) -> 0 1 2 3 4 5 6 7 8 9
* range( 5, 10 ) -> 5 6 7 8 9
* range( 0, 10, 3 ) -> 0 3 6 9
* range( '0', '9' ) -> 012345678

With an extended for loop it is possible to use such a feature too:



/*

 * This project is made available under the terms of the BSD license, more information can be found at

 * http://www.opensource.org/licenses/bsd-license.html

 *

 * Copyright (c) 2007. Christian Ullenboom (http://www.tutego.com/) and contributors. All rights reserved.

 */

package com.tutego;



import java.util.Iterator;



/**

 * Class that generates immutable sequences (ranges) as Iterable

 * objects. A range represents a start (0 if not given), an stop (mandatory) and

 * an optional step (1 by default). The start value is included in the range,

 * the stop value is exclusive. Every range is handled by an Iterable

 * which can by used in an extended for loop.

 * 

 * 
 * for ( int i : range( 0, 10, 3 ) )

 *   System.out.print( i + " " ); // 0 3 6 9

 * 

 * 

 * @author Christian Ullenboom (tutego)

 * @version 1.0

 */

public class Range

{

  public static Iterable range( final int start, final int stop, final int step )

  {

    if ( step <= 0 )

      throw new IllegalArgumentException( "step > 0 isrequired!" );



    return new Iterable()

    {

      public Iterator iterator()

      {

        return new Iterator()

        {

          private int counter = start;



          public boolean hasNext()

          {

            return counter < stop;

          }



          public Integer next()

          {

            try

            {

              return counter;

            }

            finally { counter += step; }

          }



          public void remove() { }

        };

      }

    };

  }



  public static Iterable range( final int start, final int stop )

  {

    return range( start, stop, 1 );

  }



  public static Iterable range( final int stop )

  {

    return range( 0, stop, 1 );

  }

}

This is an example:



package com.tutego;



import static com.tutego.Range.range;



public class RangeDemo

{

  public static void main( String[] args )

  {

    for ( int i : range( 10 ) )

      System.out.print( i + " " );



    System.out.println();



    for ( int i : range( 5, 10 ) )

      System.out.print( i + " " );



    System.out.println();



    for ( int i : range( 0, 10, 3 ) )

      System.out.print( i + " " );



    System.out.println();



    for ( int i : range( '0', '9' ) )

      System.out.print( (char) i  );



    System.out.println();



    String[] a = { "Mary", "had", "a", "little", "lamb" };

    for ( int i : range(a.length ) )

      System.out.printf( "%d %s%n", i, a[i] );

  }

}

Handy Iterable for a range of Integers

asgeirn (Asgeir S. Nilsen) — Tue, 10 Apr 2007 14:39:26 GMT

Looping a specific number of times produces code a bit too verbose in Java. The JDK5 enhanced for statement is a handy improvement, but you still have to fall back to the traditional for statement if you want to repeat a loop, say, 10 times.

Not with this implementation of Iterable. You can use it like this:



for (int i : new Range(100))

    System.out.printf("I have said this %d times. Read dzone.com!%n", i);



class Range implements Iterable {

    

    private final Integer stop;

    

    public Range(int stop) {

        this.stop = stop;

    }



    public Iterator iterator() {

        return new Iterator() {

            

            private Integer counter = 0;



            public boolean hasNext() {

                return (counter != stop);

            }



            public Integer next() {

                if (counter == stop)

                    throw new NoSuchElementException();

                return ++counter;

            }



            public void remove() {

            }};

    }

    

}

DZone Snippets: jdk5 code

range() in Java

Handy Iterable for a range of Integers