blob: 686d7501e6b1c7337b3859142e5607d9237e1614 [file] [log] [blame]
package com.googlecode.prolog_cafe.lang;
/**
* Trail stack.<br>
* The class <code>Trail</code> represents a trail stack.<br>
* Entries pushed to this trail stack must implement
* the <code>Undoable</code> interface.
* @see Undoable
* @author Mutsunori Banbara (banbara@kobe-u.ac.jp)
* @author Naoyuki Tamura (tamura@kobe-u.ac.jp)
* @version 1.0
*/
public final class Trail {
/** An array of <code>Undoable</code> entries. */
private Undoable[] buffer;
/** the top index of this <code>Trail</code>. */
private int top;
/** Current timestamp of the top of {@link ChoicePointStack}. */
long timeStamp;
/** Constructs a new trail stack. */
public Trail() {
this(20000);
}
/** Constructs a new trail stack with the given size. */
public Trail(int n) {
buffer = new Undoable[n];
top = -1;
}
/** Discards all entries. */
public void init() { deleteAll(); }
/** Pushs an entry to this <code>Trail</code>. */
public void push(Undoable t) {
try {
buffer[++top] = t;
} catch (ArrayIndexOutOfBoundsException e) {
int len = buffer.length;
Undoable[] new_buffer = new Undoable[len+20000];
System.arraycopy(buffer, 0, new_buffer, 0, len);
buffer = new_buffer;
buffer[top] = t;
}
}
/** Pops an entry from this <code>Trail</code>. */
public Undoable pop() {
Undoable t = buffer[top];
buffer[top--] = null;
return t;
}
/** Discards all entries. */
protected void deleteAll() {
while (! empty()) {
buffer[top--] = null;
}
}
/** Tests if this stack has no entry. */
public boolean empty() {
return top == -1;
}
/** Current allocation of the trail storage array. */
public int max() { return buffer.length; }
/** Returns the value of <code>top</code>.
* @see #top
*/
public int top() { return top; }
/** Unwinds all entries after the value of <code>i</code>. */
public void unwind(int i) {
Undoable t;
while (top > i) {
t = pop();
t.undo();
}
}
/** Shows the contents of this <code>Trail</code>. */
public void show() {
if (empty()) {
System.out.println("{trail stack is empty!}");
return;
}
for (int i=0; i<=top; i++) {
System.out.print("trail[" + i + "]: ");
System.out.println(buffer[i]);
}
}
}