operators
Class PSLineto

java.lang.Object
  operators.PSLineto

All Implemented Interfaces:

PSObject, PSOperator, PSPathOperator

public class PSLineto

extends java.lang.Object

implements PSPathOperator

Implements PSPathOperator interface.

Methods such as getOperatorToken() are inherited from PSPathOperator interface which, in turn, are inherited from PSOperator. This concrete class is responsible for adding a line to the contents of the Graphics Stack which describes a line between the current position and the coordinates given.

Before adding the line command, action() has to check if there are 2 PSNumber literals on top of the runtime stack and also if the current position is not null.

Constructor Summary

PSLineto()

Method Summary

void	action(PSStack s, PSPath p) Creates a new DrawableLine and adds it to the contents of the Graphics 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

PSLineto

public PSLineto()

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 "lineto".

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 line can occur if the coordinates have been given and the current position is not null.

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,
                   PSPath p)

Creates a new DrawableLine and adds it to the contents of the Graphics Stack.

Precondition : A valid Runtime Stack is given to method with 2 PSNumber literals on top and a valid Graphics Stack with the current position not set to null.
Postcondition : The line will be added to the contents of the Graphics Stack from the current position to the coordinates given (y comes before x). It also updates the variable holding the current position.

Specified by:

action in interface PSPathOperator

Parameters:

s - The Runtime Stack which holds the coordinates.

p - The Graphics Stack.