Growable Object stack with type specific access methods
/*
Copyright (c) 2000-2006, Dennis M. Sosnoski
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are permitted provided that the following conditions are met:
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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*/
import java.lang.reflect.Array;
/**
* Growable <code>Object</code> stack with type specific access methods. This
* implementation is unsynchronized in order to provide the best possible
* performance for typical usage scenarios, so explicit synchronization must
* be implemented by a wrapper class or directly by the application in cases
* where instances are modified in a multithreaded environment.
*
* @author Dennis M. Sosnoski
*/
public class ObjectStack
{
/** Default initial array size. */
public static final int DEFAULT_SIZE = 8;
/** Size of the current array. */
protected int m_countLimit;
/** The number of values currently present in the stack. */
protected int m_countPresent;
/** Maximum size increment for growing array. */
protected int m_maximumGrowth;
/** The underlying array used for storing the data. */
protected Object[] m_baseArray;
/**
* Constructor with full specification.
*
* @param size number of <code>Object</code> values initially allowed in
* stack
* @param growth maximum size increment for growing stack
*/
public ObjectStack(int size, int growth) {
m_countLimit = size;
m_maximumGrowth = growth;
m_baseArray = new Object[size];
}
/**
* Constructor with initial size specified.
*
* @param size number of <code>Object</code> values initially allowed in
* stack
*/
public ObjectStack(int size) {
this(size, Integer.MAX_VALUE);
}
/**
* Default constructor.
*/
public ObjectStack() {
this(DEFAULT_SIZE);
}
/**
* Copy (clone) constructor.
*
* @param base instance being copied
*/
public ObjectStack(ObjectStack base) {
this(base.m_countLimit, base.m_maximumGrowth);
System.arraycopy(base.m_baseArray, 0, m_baseArray, 0,
base.m_countPresent);
m_countPresent = base.m_countPresent;
}
/**
* Constructor from array of strings.
*
* @param strings array of strings for initial contents
*/
public ObjectStack(Object[] strings) {
this(strings.length);
System.arraycopy(strings, 0, m_baseArray, 0, strings.length);
m_countPresent = strings.length;
}
/**
* Copy data after array resize. This just copies the entire contents of the
* old array to the start of the new array. It should be overridden in cases
* where data needs to be rearranged in the array after a resize.
*
* @param base original array containing data
* @param grown resized array for data
*/
private void resizeCopy(Object base, Object grown) {
System.arraycopy(base, 0, grown, 0, Array.getLength(base));
}
/**
* Discards values for a range of indices in the array. Checks if the
* values stored in the array are object references, and if so clears
* them. If the values are primitives, this method does nothing.
*
* @param from index of first value to be discarded
* @param to index past last value to be discarded
*/
private void discardValues(int from, int to) {
for (int i = from; i < to; i++) {
m_baseArray[i] = null;
}
}
/**
* Increase the size of the array to at least a specified size. The array
* will normally be at least doubled in size, but if a maximum size
* increment was specified in the constructor and the value is less than
* the current size of the array, the maximum increment will be used
* instead. If the requested size requires more than the default growth,
* the requested size overrides the normal growth and determines the size
* of the replacement array.
*
* @param required new minimum size required
*/
private void growArray(int required) {
int size = Math.max(required,
m_countLimit + Math.min(m_countLimit, m_maximumGrowth));
Object[] grown = new Object[size];
resizeCopy(m_baseArray, grown);
m_countLimit = size;
m_baseArray = grown;
}
/**
* Ensure that the array has the capacity for at least the specified
* number of values.
*
* @param min minimum capacity to be guaranteed
*/
public final void ensureCapacity(int min) {
if (min > m_countLimit) {
growArray(min);
}
}
/**
* Push a value on the stack.
*
* @param value value to be added
*/
public void push(Object value) {
int index = getAddIndex();
m_baseArray[index] = value;
}
/**
* Pop a value from the stack.
*
* @return value from top of stack
* @exception ArrayIndexOutOfBoundsException on attempt to pop empty stack
*/
public Object pop() {
if (m_countPresent > 0) {
Object value = m_baseArray[--m_countPresent];
m_baseArray[m_countPresent] = null;
return value;
} else {
throw new ArrayIndexOutOfBoundsException
("Attempt to pop empty stack");
}
}
/**
* Pop multiple values from the stack. The last value popped is the
* one returned.
*
* @param count number of values to pop from stack (must be strictly
* positive)
* @return value from top of stack
* @exception ArrayIndexOutOfBoundsException on attempt to pop past end of
* stack
*/
public Object pop(int count) {
if (count < 0) {
throw new IllegalArgumentException("Count must be greater than 0");
} else if (m_countPresent >= count) {
m_countPresent -= count;
Object value = m_baseArray[m_countPresent];
discardValues(m_countPresent, m_countPresent + count);
return value;
} else {
throw new ArrayIndexOutOfBoundsException
("Attempt to pop past end of stack");
}
}
/**
* Copy a value from the stack. This returns a value from within
* the stack without modifying the stack.
*
* @param depth depth of value to be returned
* @return value from stack
* @exception ArrayIndexOutOfBoundsException on attempt to peek past end of
* stack
*/
public Object peek(int depth) {
if (m_countPresent > depth) {
return m_baseArray[m_countPresent - depth - 1];
} else {
throw new ArrayIndexOutOfBoundsException
("Attempt to peek past end of stack");
}
}
/**
* Copy top value from the stack. This returns the top value without
* removing it from the stack.
*
* @return value at top of stack
* @exception ArrayIndexOutOfBoundsException on attempt to peek empty stack
*/
public Object peek() {
return peek(0);
}
/**
* Constructs and returns a simple array containing the same data as held
* in this stack. Note that the items will be in reverse pop order, with
* the last item to be popped from the stack as the first item in the
* array.
*
* @return array containing a copy of the data
*/
public Object[] toArray() {
Object[] copy = new Object[m_countPresent];
System.arraycopy(m_baseArray, 0, copy, 0, m_countPresent);
return copy;
}
/**
* Duplicates the object with the generic call.
*
* @return a copy of the object
*/
public Object clone() {
return new ObjectStack(this);
}
/**
* Gets the array offset for appending a value to those in the stack.
* If the underlying array is full, it is grown by the appropriate size
* increment so that the index value returned is always valid for the
* array in use by the time of the return.
*
* @return index position for added element
*/
private int getAddIndex() {
int index = m_countPresent++;
if (m_countPresent > m_countLimit) {
growArray(m_countPresent);
}
return index;
}
/**
* Get the number of values currently present in the stack.
*
* @return count of values present
*/
public int size() {
return m_countPresent;
}
/**
* Check if stack is empty.
*
* @return <code>true</code> if stack empty, <code>false</code> if not
*/
public boolean isEmpty() {
return m_countPresent == 0;
}
/**
* Set the stack to the empty state.
*/
public void clear() {
discardValues(0, m_countPresent);
m_countPresent = 0;
}
}
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