slogo.instruction

Class Difference

java.lang.Object

slogo.GrammarElement

slogo.instruction.Instruction

slogo.instruction.Difference

public class Difference
extends Instruction

A DIFFERENCE instruction has two components: two GrammarElements that represents the two numbers to perform subtraction on. To evaluate a DIFFERENCE instruction the expressions are evaluated first, this determines the double version of the numbers. The second number is subtracted from the first and the result is returned.

The value returned by evaluating a DIFFERENCE instruction is the instruction itself, followed by the two expressions

Field Summary

Fields

Modifier and Type	Field and Description
private GrammarElement	expressionOne
private GrammarElement	expressionTwo

Fields inherited from class slogo.GrammarElement

gelementsToValue

Constructor Summary

Constructors

Constructor and Description
Difference(GrammarElement e, GrammarElement f) Constructs a DIFFERENCE instruction that can be executed.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	evaluate(Context c) Evaluate this instruction in a Context.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

expressionOne

private GrammarElement expressionOne

expressionTwo

private GrammarElement expressionTwo

Constructor Detail

Difference

public Difference(GrammarElement e,
                  GrammarElement f)

Constructs a DIFFERENCE instruction that can be executed.

Parameters:

e - the first number

f - the second number

Method Detail

evaluate

public java.lang.Object evaluate(Context c)

Evaluate this instruction in a Context.

Specified by:

evaluate in class Instruction

Parameters:

c - the Context for the evaluation

Returns:

the total after subtraction

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

Returns:

a String representing this instruction as DIFFERNCE, followed by the two expressions