freegraph
Class ExpressionItem

java.lang.Object
  |
  +--freegraph.ExpressionItem

Direct Known Subclasses:

ExpressionItem.BiOperator, ExpressionItem.Number, ExpressionItem.Parenthesis, ExpressionItem.UnOperator, ExpressionItem.Variable

public abstract class ExpressionItem

extends java.lang.Object

Instances of ExpressionItem are used internally by the package. The base class ExpressionItem's getAction() is used polymorphically when converting from infix to RPN. The method returns an integer corresponding to the operation code to perform when converting from infix to RPN. Each implementation is a simple class to hold an operator, number, variable, or parenthesis.

Although the base class is used polymorphically by ExpressionStack for conversion to RPN, the various ExpressionItems are downcast when evaluated by ExpressionEvaluator.

This class is used internally by the package. It was exposed as public so that classes outside of the package can use ExpressionStack, and so Applets such as ExpressionParsingApplet could be made outside the package.

The algorithm used is from: Tanenbaum, Andrew S. 1990. Structured Computer Organization, 3rd ed., New Jersey: Prentice Hall. (pp. 268-272)

See Also:

ExpressionStack, ExpressionEvaluator

Nested Class Summary

static class	ExpressionItem.BiOperator A BiOperator is an ExpressionItem used to hold a all binary operators.
static class	ExpressionItem.Number NumberExpressionItem is an ExpressionItem to represent a literal Number.
static class	ExpressionItem.Parenthesis A Parenthesis is an ExpressionItem used to hold a single parenthesis.
static class	ExpressionItem.UnOperator A UnOperator is an ExpressionItem used to hold a all unary operators.
static class	ExpressionItem.Variable A VariableExpressionItem is an ExpressionItem used to hold a single character variable.

Constructor Summary

ExpressionItem()

Method Summary

abstract int

getAction(ExpressionItem exprItem)

Methods inherited from class java.lang.Object

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

Constructor Detail

ExpressionItem

public ExpressionItem()

Method Detail

getAction

public abstract int getAction(ExpressionItem exprItem)