SizeSequence

Class Overview

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.

Summary

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

Public Methods
int	getIndex(int position) Returns the index of the entry that corresponds to the specified position.
int	getPosition(int index) Returns the start position for the specified entry.
int	getSize(int index) Returns the size of the specified entry.
int[]	getSizes() Returns the size of all entries.
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.

[Expand] Inherited Methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object. final void wait(long timeout, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long timeout) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed.