intglide.java

java高级使用教程 全书一共分六章

// IntGlide - randomly glide an int around within a specified range
//
// Copyright (C) 1996 by Jef Poskanzer <[e-mail]>.  All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.

package Acme;

import java.util.*;

/// Randomly glide an int around within a specified range.
// <P>
// <A HREF="/resources/classes/Acme/IntGlide.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>

public class IntGlide
    {
    private final int scale = 32;
    private int low, high, maxdelta, value;
    private int delta;
    private static Random random = new Random();

    /// Constructor.
    public IntGlide( int low, int high, int maxdelta, int value )
	{
	this.low = low * scale;
	this.high = high * scale;
	this.maxdelta = maxdelta * scale;
	this.value = value * scale;
	validate();
	newDelta();
	}

    /// Constructor, unspecified initial value.
    public IntGlide( int low, int high, int maxdelta )
	{
	this(
	    low, high, maxdelta,
	    ( Math.abs( random.nextInt() ) % ( high - low + 1 ) ) + low );
	}

    private void validate()
	{
	if ( high < low )
	    {
	    int t = high;
	    high = low;
	    low = t;
	    }
	if ( maxdelta < 1 )
	    maxdelta = 1;
	}

    /// Return the next value in the sequence.
    public int next()
	{
	int newval;
	for ( int i = 0; i < 10; ++i )
	    {
	    newval = value + delta;
	    if ( newval >= low && newval <= high )
		{
		value = newval;
		return value / scale;
		}
	    newDelta();
	    }
	if ( value < low )
	    value = low;
	else if ( value > high )
	    value = high;
	return value / scale;
	}

    private void newDelta()
	{
	delta = ( Math.abs( random.nextInt() ) % ( maxdelta * 2 ) ) - maxdelta;
	if ( delta <= 0 )
	    --delta;
	}
    }