operators
Class PSDup

java.lang.Object
  operators.PSDup

All Implemented Interfaces:

PSObject, PSOperator, PSStackOperator

public class PSDup

extends java.lang.Object

implements PSStackOperator

Implements PSStackOperator interface.

Methods such as getOperatorToken() are inherited by PSStackOperator interface which in turn, are inherited by PSOperator.This concrete class is responsible for the dublication of the top element found in stack.

Constructor Summary

PSDup()

Method Summary

void	action(PSStack s) Dublicates the top element of the stack.
java.lang.String	getOperatorToken() Returns the token identifying this operator.
boolean	isValid(PSStack s) Checks if it valid to use this operator now.

Methods inherited from class java.lang.Object

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

Constructor Detail

PSDup

public PSDup()

Method Detail

getOperatorToken

public java.lang.String getOperatorToken()

Returns the token identifying this operator.

Returns the name of the operand that this concrete class simulates,here "dup".

Precondition : A valid operator class has been created.
Postcondition : A string is returned,labeling the semantics of this class.

Specified by:

getOperatorToken in interface PSOperator

Returns:

The token identifying this operator.

isValid

public boolean isValid(PSStack s)
                throws PSSyntaxException

Checks if it valid to use this operator now.

The dublication can occur only if the stack contains at least one element.

Precondition : A valid instance of PSStack is given.
Postcondition : A reply to whether the elements of the stack can be removed.

Specified by:

isValid in interface PSOperator

Parameters:

s - A reference to a PSStack instance.

Returns:

True if the operation can be performed,false otherwise.

Throws:

PSSyntaxException - The syntax of the token is wrong.

action

public void action(PSStack s)

Dublicates the top element of the stack.

Dublicates the top element of the stack.

Precondition : A valid stack is given to method.
Postcondition : Dublication of the top element.

Specified by:

action in interface PSStackOperator

Parameters:

s - The Run-time Stack which will be evacuated