javax.swing
Class SizeSequence

java.lang.Object
  javax.swing.SizeSequence

public class SizeSequence

extends Object

A SizeSequence object efficiently maintains an ordered list of sizes and corresponding positions. One situation for which SizeSequence might be appropriate is in a component that displays multiple rows of unequal size. In this case, a single SizeSequence object could be used to track the heights and Y positions of all rows.

Another example would be a multi-column component, such as a JTable, in which the column sizes are not all equal. The JTable might use a single SizeSequence object to store the widths and X positions of all the columns. The JTable could then use the SizeSequence object to find the column corresponding to a certain position. The JTable could update the SizeSequence object whenever one or more column sizes changed.

The following figure shows the relationship between size and position data for a multi-column component.

In the figure, the first index (0) corresponds to the first column, the second index (1) to the second column, and so on. The first column's position starts at 0, and the column occupies size₀ pixels, where size₀ is the value returned by getSize(0). Thus, the first column ends at size₀ - 1. The second column then begins at the position size₀ and occupies size₁ (getSize(1)) pixels.

Note that a SizeSequence object simply represents intervals along an axis. In our examples, the intervals represent height or width in pixels. However, any other unit of measure (for example, time in days) could be just as valid.

Implementation Notes

Normally when storing the size and position of entries, one would choose between storing the sizes or storing their positions instead. The two common operations that are needed during rendering are: getIndex(position) and setSize(index, size). Whichever choice of internal format is made one of these operations is costly when the number of entries becomes large. If sizes are stored, finding the index of the entry that encloses a particular position is linear in the number of entries. If positions are stored instead, setting the size of an entry at a particular index requires updating the positions of the affected entries, which is also a linear calculation.

Like the above techniques this class holds an array of N integers internally but uses a hybrid encoding, which is halfway between the size-based and positional-based approaches. The result is a data structure that takes the same space to store the information but can perform most operations in Log(N) time instead of O(N), where N is the number of entries in the list.

Two operations that remain O(N) in the number of entries are the insertEntries and removeEntries methods, both of which are implemented by converting the internal array to a set of integer sizes, copying it into the new array, and then reforming the hybrid representation in place.

Author:

Philip Milne

Field Summary

private int[]	a
private static int[]	emptyArray

Constructor Summary

SizeSequence()
Creates a new SizeSequence object that contains no entries.

SizeSequence(int numEntries)
Creates a new SizeSequence object that contains the specified number of entries, all initialized to have size 0.

SizeSequence(int[] sizes)
Creates a new SizeSequence object that contains the specified sizes.

SizeSequence(int numEntries, int value)
Creates a new SizeSequence object that contains the specified number of entries, all initialized to have size value.

Method Summary

private void	changeSize(int from, int to, int index, int delta)
int	getIndex(int position) Returns the index of the entry that corresponds to the specified position.
private int	getIndex(int from, int to, int position)
int	getPosition(int index) Returns the start position for the specified entry.
private int	getPosition(int from, int to, int index)
int	getSize(int index) Returns the size of the specified entry.
int[]	getSizes() Returns the size of all entries.
private int	getSizes(int from, int to, int[] sizes)
void	insertEntries(int start, int length, int value) Adds a contiguous group of entries to this SizeSequence.
void	removeEntries(int start, int length) Removes a contiguous group of entries from this SizeSequence.
void	setSize(int index, int size) Sets the size of the specified entry.
void	setSizes(int[] sizes) Resets this SizeSequence object, using the data in the sizes argument.
private int	setSizes(int from, int to, int[] sizes)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

emptyArray

private static int[] emptyArray

a

private int[] a

Constructor Detail

SizeSequence

public SizeSequence()

Creates a new SizeSequence object that contains no entries. To add entries, you can use insertEntries or setSizes.

See Also:

insertEntries(int, int, int), setSizes(int[])

SizeSequence

public SizeSequence(int numEntries)

Creates a new SizeSequence object that contains the specified number of entries, all initialized to have size 0.

Parameters:

numEntries - the number of sizes to track

Throws:

NegativeArraySizeException - if numEntries < 0

SizeSequence

public SizeSequence(int numEntries,
                    int value)

Creates a new SizeSequence object that contains the specified number of entries, all initialized to have size value.

Parameters:

numEntries - the number of sizes to track

value - the initial value of each size

SizeSequence

public SizeSequence(int[] sizes)

Creates a new SizeSequence object that contains the specified sizes.

Parameters:

sizes - the array of sizes to be contained in the SizeSequence

Method Detail

setSizes

public void setSizes(int[] sizes)

Resets this SizeSequence object, using the data in the sizes argument. This method reinitializes this object so that it contains as many entries as the sizes array. Each entry's size is initialized to the value of the corresponding item in sizes.

Parameters:

sizes - the array of sizes to be contained in this SizeSequence

setSizes

private int setSizes(int from,
                     int to,
                     int[] sizes)

getSizes

public int[] getSizes()

Returns the size of all entries.

Returns:

a new array containing the sizes in this object

getSizes

private int getSizes(int from,
                     int to,
                     int[] sizes)

getPosition

public int getPosition(int index)

Returns the start position for the specified entry. For example, getPosition(0) returns 0, getPosition(1) is equal to getSize(0), getPosition(2) is equal to getSize(0) + getSize(1), and so on.

Note that if index is greater than length the value returned may be meaningless.

Parameters:

index - the index of the entry whose position is desired

Returns:

the starting position of the specified entry

getPosition

private int getPosition(int from,
                        int to,
                        int index)

getIndex

public int getIndex(int position)

Returns the index of the entry that corresponds to the specified position. For example, getIndex(0) is 0, since the first entry always starts at position 0.

Parameters:

position - the position of the entry

Returns:

the index of the entry that occupies the specified position

getIndex

private int getIndex(int from,
                     int to,
                     int position)

getSize

public int getSize(int index)

Returns the size of the specified entry. If index is out of the range (0 <= index < getSizes().length) the behavior is unspecified.

Parameters:

index - the index corresponding to the entry

Returns:

the size of the entry

setSize

public void setSize(int index,
                    int size)

Sets the size of the specified entry. Note that if the value of index does not fall in the range: (0 <= index < getSizes().length) the behavior is unspecified.

Parameters:

index - the index corresponding to the entry

size - the size of the entry

changeSize

private void changeSize(int from,
                        int to,
                        int index,
                        int delta)

insertEntries

public void insertEntries(int start,
                          int length,
                          int value)

Adds a contiguous group of entries to this SizeSequence. Note that the values of start and length must satisfy the following conditions: (0 <= start < getSizes().length) AND (length >= 0). If these conditions are not met, the behavior is unspecified and an exception may be thrown.

Parameters:

start - the index to be assigned to the first entry in the group

length - the number of entries in the group

value - the size to be assigned to each new entry

Throws:

ArrayIndexOutOfBoundsException - if the parameters are outside of the range: (0 <= start < (getSizes().length)) AND (length >= 0)

removeEntries

public void removeEntries(int start,
                          int length)

Removes a contiguous group of entries from this SizeSequence. Note that the values of start and length must satisfy the following conditions: (0 <= start < getSizes().length) AND (length >= 0). If these conditions are not met, the behavior is unspecified and an exception may be thrown.

Parameters:

start - the index of the first entry to be removed

length - the number of entries to be removed