operators
Class PSShow

java.lang.Object
  operators.PSShow

All Implemented Interfaces:

PSObject, PSOperator, PSStringOperator

public class PSShow

extends java.lang.Object

implements PSStringOperator

Implements PSStringOperator interface.

Methods such as getOperatorToken() are inherited from PSStringOperator interface which, in turn, are inherited from PSOperator. This concrete class is responsible for drawing a string at the curent position on the Graphics Machine.

Constructor Summary

PSShow()

Method Summary

void	action(PSStack s) Calls DrawableString which performs the actual drawing on the screen.
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

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

Constructor Detail

PSShow

public PSShow()

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 "show".

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 drawing of a string can occur only if there is a string on top of the Runtime Stack and a current position has been defined.

Precondition : A valid instance of PSStack.
Postcondition : A reply to the question whether the operator can perfom its defined behaviour.

Specified by:

isValid in interface PSOperator

Parameters:

s - A reference to PSStack instance.

Returns:

True if the operation can be executed, false otherwise.

Throws:

PSSyntaxException - The syntax of the token is wrong.

action

public void action(PSStack s)

Calls DrawableString which performs the actual drawing on the screen.

Precondition : A valid Runtime Stack is given to method with a PSString on top and the current position is not null.
Postcondition : The string will be drawn at the current position.

Specified by:

action in interface PSStringOperator

Parameters:

s - The Runtime Stack which holds the PSString.