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A collection of Java utilities.
//
// samskivert library - useful routines for java programs
// Copyright (C) 2001-2012 Michael Bayne, et al.
// http://github.com/samskivert/samskivert/blob/master/COPYING
package com.samskivert.util;
/**
* List util is for the times when you just can't bear the overhead of an
* {@link java.util.ArrayList} object to manage your list of objects. It
* provides a suite of list management routines that operate on bare
* {@link java.lang.Object} arrays. Some of those routines mimic the
* behavior of array lists, others provide other more specialized
* (generally faster but making requirements of the caller) list behavior.
*
* An example is probably in order:
*
*
* Object[] list = null;
* String foo = "foo";
* String bar = "bar";
*
* // add our objects to a list
* list = ListUtil.add(list, foo);
* list = ListUtil.add(list, bar);
*
* // remove foo from the list (does so by clearing out that index, but it
* // doesn't slide subsequent elements down)
* ListUtil.clear(list, foo);
*
* // use the version of remove that calls equals() rather than just
* // checking for equality of references
* String anotherBar = "bar";
* ListUtil.clear(list, anotherBar);
*
* // append our objects to the end of the list letting list util know
* // that we're tracking the list size
* list = ListUtil.add(list, 0, foo);
* list = ListUtil.add(list, 1, bar);
*
* // remove the elements from the list, compacting it to preserve
* // element continuity
* ListUtil.remove(list, 0);
* ListUtil.remove(list, bar);
*
*
* See the documentation for the individual functions for their exact
* behavior.
*/
public class ListUtil
{
/**
* Rounds the specified value up to the next nearest power of two.
*/
public static int nextPowerOfTwo (int value)
{
return (int)Math.pow(2, Math.ceil(Math.log(value) / Math.log(2)));
}
/**
* Adds the specified element to the first empty slot in the specified
* list. Begins searching for empty slots at zeroth index.
*
* @param list the list to which to add the element. Can be null.
* @param element the element to add.
*
* @return a reference to the list with element added (might not be
* the list you passed in due to expansion, or allocation).
*/
public static Object[] add (Object[] list, Object element)
{
return add(list, 0, element);
}
/**
* Adds the specified element to the next empty slot in the specified
* list. Begins searching for empty slots at the specified index. This
* can be used to quickly add elements to a list that preserves
* consecutivity by calling it with the size of the list as the first
* index to check.
*
* @param list the list to which to add the element. Can be null.
* @param startIdx the index at which to start looking for a spot.
* @param element the element to add.
*
* @return a reference to the list with element added (might not be
* the list you passed in due to expansion, or allocation).
*/
public static Object[] add (Object[] list, int startIdx, Object element)
{
requireNotNull(element);
// make sure we've got a list to work with
if (list == null) {
list = new Object[DEFAULT_LIST_SIZE];
}
// search for a spot to insert yon element; assuming we'll insert
// it at the end of the list if we don't find one
int llength = list.length;
int index = llength;
for (int i = startIdx; i < llength; i++) {
if (list[i] == null) {
index = i;
break;
}
}
// expand the list if necessary
if (index >= llength) {
list = accomodate(list, index);
}
// stick the element on in
list[index] = element;
return list;
}
/**
* Inserts the supplied element at the specified position in the
* array, shifting the remaining elements down. The array will be
* expanded if necessary.
*
* @param list the list in which to insert the element. Can be null.
* @param index the index at which to insert the element.
* @param element the element to insert.
*
* @return a reference to the list with element inserted (might not be
* the list you passed in due to expansion, or allocation).
*/
public static Object[] insert (Object[] list, int index, Object element)
{
requireNotNull(element);
// make sure we've got a list to work with
if (list == null) {
list = new Object[DEFAULT_LIST_SIZE];
}
// make a note of the size of the array
int size = list.length;
// expand the list if necessary (the last element contains a
// value)
if (list[size-1] != null) {
list = accomodate(list, size);
} else {
// otherwise, pretend the list is one element shorter and
// we'll overwrite the last null
size--;
}
// shift everything down
System.arraycopy(list, index, list, index+1, size-index);
// stick the element on in
list[index] = element;
return list;
}
/**
* Searches through the list checking to see if the element supplied
* is already in the list (using reference equality to check for
* existence) and adds it if it is not.
*
* @param list the list to which to add the element. Can be null.
* @param element the element to test and add.
*
* @return a reference to the list with element added (might not be
* the list you passed in due to expansion, or allocation) or null if
* the element was already in the original array.
*/
public static Object[] testAndAddRef (Object[] list, Object element)
{
return testAndAdd(REFERENCE_COMP, list, element);
}
/**
* Searches through the list checking to see if the element supplied
* is already in the list (using equals() to check for
* equality) and adds it if it is not.
*
* @param list the list to which to add the element. Can be null.
* @param element the element to test and add.
*
* @return a reference to the list with element added (might not be
* the list you passed in due to expansion, or allocation) or null if
* the element was already in the original array.
*/
public static Object[] testAndAdd (Object[] list, Object element)
{
return testAndAdd(EQUALS_COMP, list, element);
}
/** Helper function for {@link #testAndAddRef}, etc. */
protected static Object[] testAndAdd (
EqualityComparator eqc, Object[] list, Object element)
{
requireNotNull(element);
// make sure we've got a list to work with
if (list == null) {
list = new Object[DEFAULT_LIST_SIZE];
}
// search for a spot to insert yon element; we'll insert it at the
// end of the list if we don't find a spot
int llength = list.length;
int index = llength;
for (int i = 0; i < llength; i++) {
Object elem = list[i];
if (elem == null) {
// only update our target index if we haven't already
// found a spot to put the element
if (index == llength) {
index = i;
}
} else if (eqc.equals(element, elem)) {
// oops, it's already in the list
return null;
}
}
// expand the list if necessary
if (index >= llength) {
list = accomodate(list, index);
}
// stick the element on in
list[index] = element;
return list;
}
/**
* Looks for an object that is referentially equal to the supplied
* element (list[idx] == element).
*
* @return true if a matching element was found, false otherwise.
*/
public static boolean containsRef (Object[] list, Object element)
{
return contains(REFERENCE_COMP, list, element);
}
/**
* Looks for an element that is functionally equal to the supplied
* element (element.equals(list[idx])).
*
* @return true if a matching element was found, false otherwise.
*/
public static boolean contains (Object[] list, Object element)
{
return contains(EQUALS_COMP, list, element);
}
/** Helper function for {@link #containsRef}, etc. */
protected static boolean contains (
EqualityComparator eqc, Object[] list, Object element)
{
return (-1 != indexOf(eqc, list, element));
}
/**
* Returns the lowest index in the array that contains null,
* or -1 if there is no room to add elements without expanding the array.
*/
public static int indexOfNull (Object[] list)
{
if (list != null) {
for (int ii=0, nn = list.length; ii < nn; ii++) {
if (list[ii] == null) {
return ii;
}
}
}
return -1;
}
/**
* Looks for an object that is referentially equal to the supplied
* element (list[idx] == element) and returns its index
* in the array.
*
* @return the index of the first matching element if one was found,
* -1 otherwise.
*/
public static int indexOfRef (Object[] list, Object element)
{
return indexOf(REFERENCE_COMP, list, element);
}
/**
* Looks for an element that is functionally equal to the supplied
* element (element.equals(list[idx])).
*
* @return the index of the matching element if one was found, -1
* otherwise.
*/
public static int indexOf (Object[] list, Object element)
{
return indexOf(EQUALS_COMP, list, element);
}
/** Helper function for {@link #indexOfRef}, etc. */
protected static int indexOf (
EqualityComparator eqc, Object[] list, Object element)
{
requireNotNull(element);
if (list != null) {
for (int ii = 0, nn = list.length; ii < nn; ii++) {
if (eqc.equals(element, list[ii])) {
return ii;
}
}
}
return -1;
}
/**
* Clears out the first element that is referentially equal to the
* supplied element (list[idx] == element).
*
* @return the element that was removed or null if it was not found.
*/
public static Object clearRef (Object[] list, Object element)
{
return clear(REFERENCE_COMP, list, element);
}
/**
* Clears out the first element that is functionally equal to the
* supplied element (element.equals(list[idx])).
*
* @return the object that was cleared from the array or null if no
* matching object was found.
*/
public static Object clear (Object[] list, Object element)
{
return clear(EQUALS_COMP, list, element);
}
/** Helper function for {@link #clearRef}, etc. */
protected static Object clear (
EqualityComparator eqc, Object[] list, Object element)
{
int dex = indexOf(eqc, list, element);
if (dex == -1) {
return null;
}
Object elem = list[dex];
list[dex] = null;
return elem;
}
/**
* Removes the first element that is referentially equal to the
* supplied element (list[idx] == element). The elements
* after the removed element will be slid down the array one spot to
* fill the place of the removed element.
*
* @return the object that was removed from the array or null if no
* matching object was found.
*/
public static Object removeRef (Object[] list, Object element)
{
return remove(REFERENCE_COMP, list, element);
}
/**
* Removes the first element that is functionally equal to the
* supplied element (element.equals(list[idx])). The
* elements after the removed element will be slid down the array one
* spot to fill the place of the removed element.
*
* @return the object that was removed from the array or null if no
* matching object was found.
*/
public static Object remove (Object[] list, Object element)
{
return remove(EQUALS_COMP, list, element);
}
/** Helper function for {@link #removeRef}, etc. */
protected static Object remove (
EqualityComparator eqc, Object[] list, Object element)
{
return remove(list, indexOf(eqc, list, element));
}
/**
* Removes the element at the specified index. The elements after the
* removed element will be slid down the array one spot to fill the
* place of the removed element. If a null array is supplied or one
* that is not large enough to accomodate this index, null is
* returned.
*
* @return the object that was removed from the array or null if no
* object existed at that location.
*/
public static Object remove (Object[] list, int index)
{
if (list == null) {
return null;
}
int llength = list.length;
if (llength <= index || index < 0) {
return null;
}
Object elem = list[index];
System.arraycopy(list, index+1, list, index, llength-(index+1));
list[llength-1] = null;
return elem;
}
/**
* Returns the number of elements prior to the first null in the supplied list.
* @deprecated This is incompatible with things like clearRef(), which leave a null space.
*/
@Deprecated public static int size (Object[] list)
{
if (list == null) {
return 0;
}
int llength = list.length;
for (int ii = 0; ii < llength; ii++) {
if (list[ii] == null) {
return ii;
}
}
return llength;
}
/**
* Returns the number of non-null elements in the supplied list.
*/
public static int getSize (Object[] list)
{
int size = 0;
for (int ii = 0, nn = (list == null) ? 0 : list.length; ii < nn; ii++) {
if (list[ii] != null) {
size++;
}
}
return size;
}
/**
* Creates a new list that will accomodate the specified index and
* copies the contents of the old list to the first.
*/
protected static Object[] accomodate (Object[] list, int index)
{
int size = list.length;
// expand size by powers of two until we're big enough
while (size <= index) {
size = Math.max(size * 2, DEFAULT_LIST_SIZE);
}
// create a new list and copy the contents
Object[] newlist = new Object[size];
System.arraycopy(list, 0, newlist, 0, list.length);
return newlist;
}
/**
* Throws a NullPointerException if the element is null.
*/
protected static void requireNotNull (Object element)
{
if (element == null) {
throw new NullPointerException("ListUtil does not support null elements.");
}
}
/**
* Run some tests.
*/
public static void main (String[] args)
{
Object[] list = null;
String foo = "foo";
String bar = "bar";
list = ListUtil.add(list, foo);
System.out.println("add(foo): " + StringUtil.toString(list));
list = ListUtil.add(list, bar);
System.out.println("add(bar): " + StringUtil.toString(list));
ListUtil.clearRef(list, foo);
System.out.println("clear(foo): " + StringUtil.toString(list));
String newBar = new String("bar"); // prevent java from cleverly
// referencing the same string
// from the constant pool
System.out.println("containsRef(newBar): " +
ListUtil.containsRef(list, newBar));
System.out.println("contains(newBar): " +
ListUtil.contains(list, newBar));
ListUtil.clear(list, newBar);
System.out.println("clear(newBar): " + StringUtil.toString(list));
list = ListUtil.add(list, 0, foo);
list = ListUtil.add(list, 1, bar);
System.out.println("Added foo+bar: " + StringUtil.toString(list));
ListUtil.removeRef(list, foo);
System.out.println("removeRef(foo): " + StringUtil.toString(list));
list = ListUtil.add(list, 0, foo);
list = ListUtil.add(list, 1, bar);
System.out.println("Added foo+bar: " + StringUtil.toString(list));
ListUtil.remove(list, 0);
System.out.println("remove(0): " + StringUtil.toString(list));
ListUtil.remove(list, 0);
System.out.println("remove(0): " + StringUtil.toString(list));
Object[] tl = ListUtil.testAndAddRef(list, bar);
if (tl == null) {
System.out.println("testAndAddRef(bar): failed: " +
StringUtil.toString(list));
} else {
list = tl;
System.out.println("testAndAddRef(bar): added: " +
StringUtil.toString(list));
}
String biz = "biz";
tl = ListUtil.testAndAddRef(list, biz);
if (tl == null) {
System.out.println("testAndAddRef(biz): failed: " +
StringUtil.toString(list));
} else {
list = tl;
System.out.println("testAndAddRef(biz): added: " +
StringUtil.toString(list));
}
}
/** Used to allow the same code to optionally use reference equality
* and {@link Object#equals}.equality. */
protected static interface EqualityComparator
{
public boolean equals (Object o1, Object o2);
}
protected static final EqualityComparator REFERENCE_COMP = new EqualityComparator() {
public boolean equals (Object o1, Object o2) {
return o1 == o2;
}
};
protected static final EqualityComparator EQUALS_COMP = new EqualityComparator() {
public boolean equals (Object o1, Object o2) {
return ObjectUtil.equals(o1, o2);
}
};
/**
* The size of a list to create if we have to create one entirely
* from scratch rather than just expand it.
*/
protected static final int DEFAULT_LIST_SIZE = 4;
}
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