OpenJDK 27 · com.sun.java_cup.internal.runtime.virtual_parse_stack

This class implements a temporary or "virtual" parse stack that replaces the top portion of the actual parse stack (the part that has been changed by some set of operations) while maintaining its original contents. This data structure is used when the parse needs to "parse ahead" to determine if a given error recovery attempt will allow the parse to continue far enough to consider it successful. Once success or failure of parse ahead is determined the system then reverts to the original parse stack (which has not actually been modified). Since parse ahead does not execute actions, only parse state is maintained on the virtual stack, not full Symbol objects.

Field Summary

Modifier and Type	Field and Description
protected int	real_next Top of stack indicator for where we leave off in the real stack.
protected Stack<Symbol>	real_stack The real stack that we shadow.
protected Stack<Integer>	vstack The virtual top portion of the stack.

Constructor Summary

Access	Constructor and Description
public	virtual_parse_stack(Stack<Symbol> shadowing_stack) Constructor to build a virtual stack out of a real stack.

Method Summary

Modifier and Type	Method and Description
public boolean	empty() Indicate whether the stack is empty.
protected void	get_from_real() Transfer an element from the real to the virtual stack.
public void	pop() Pop the stack.
public void	push(int state_num) Push a state number onto the stack.
public int	top() Return value on the top of the stack (without popping it).

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

real_next	back to summary
protected int real_next Top of stack indicator for where we leave off in the real stack. This is measured from top of stack, so 0 would indicate that no elements have been "moved" from the real to virtual stack.

real_stack	back to summary
protected Stack<Symbol> real_stack The real stack that we shadow. This is accessed when we move off the bottom of the virtual portion of the stack, but is always left unmodified.

vstack	back to summary
protected Stack<Integer> vstack The virtual top portion of the stack. This stack contains Integer objects with state numbers. This stack shadows the top portion of the real stack within the area that has been modified (via operations on the virtual stack). When this portion of the stack becomes empty we transfer elements from the underlying stack onto this stack.

Constructor Detail

virtual_parse_stack	back to summary
public virtual_parse_stack(Stack<Symbol> shadowing_stack) throws Exception Constructor to build a virtual stack out of a real stack.

Method Detail

empty	back to summary
public boolean empty() Indicate whether the stack is empty.

get_from_real	back to summary
protected void get_from_real() Transfer an element from the real to the virtual stack. This assumes that the virtual stack is currently empty.

pop	back to summary
public void pop() throws Exception Pop the stack.

push	back to summary
public void push(int state_num) Push a state number onto the stack.