Class ExprEvaluatorTest

java.lang.Object

ExprEvaluatorTest

All Implemented Interfaces:

java.awt.event.ActionListener, java.awt.event.FocusListener, java.util.EventListener

public class ExprEvaluatorTest
extends java.lang.Object
implements java.awt.event.ActionListener, java.awt.event.FocusListener

Test application program for ExprEvaluator.java. Allows inputting t, x, and y as numbers and either a postfix, infix or postfix expression. This application is not developed nearly as well as InfixEvalDemo.java but it does allow evaluation of prefix and postfix expressions. If more than one of the prefix, infix, or postfix expressions is supplied, the application evaluates the first of the supplied expressions. If a value is assigned to a variable other than t, x, or y using the "=" operator, then the value of that variable is stored for future use.

The simple minded application alternates between two dialog boxes, one for input and one for output. The output includes the values of t, x, and y, the expression tree, and corresponding prefix and postfix expressions.

An infix expression is the typical way we write algebraic expressions that uses binary operators between the values they operate on and uses parenthesis to help determine the order of evaluation and specify arguments for functions. For example:
x * y + 20
(x-10)/(x+5)
10 * abs(x^2 - y^2)
h = sqrt(x^2 + y^2)

Postfix expressions are written with the value before the operator. This is sometimes called Reverse Polish notation and is similar to the notation used in HP calculators. It is particularly convenient for computers. For example, the above expressions would be written:
x y * 20 +
x 10 - x 5 + /
10 x 2 ^ y 2 ^ - abs *
h x 2 ^ y 2 ^ + sqrt =

Prefix expressions are written with the operator before the values it applies to. This notation is also somewhat convenient for computers but fairly rare. The above examples would be written:
+ * x y 20
/ - x 10 + x 5
* 10 abs - ^ x 2 ^ y 2
= h sqrt + ^ x 2 ^ y 2

Requires:
ExprEvaluator.java
EasyFormat.java
DoubleScanner.java

Constructor Summary

Constructors

Constructor and Description
ExprEvaluatorTest()

Method Summary

Modifier and Type	Method and Description
void	actionPerformed(java.awt.event.ActionEvent e) Used to process help and exit buttons
void	focusGained(java.awt.event.FocusEvent e) Used to select all the text whenever the JTextField gets the focus
void	focusLost(java.awt.event.FocusEvent e) Required to implement FocusListener but does not do anything.
static void	main(java.lang.String[] args) Main test program.

Methods inherited from class java.lang.Object

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

Constructor Detail

ExprEvaluatorTest

public ExprEvaluatorTest()

Method Detail

main

public static void main(java.lang.String[] args)

Main test program. Creates a Dialog for input. Calls the appropriate build method to build a tree from the expression. Then calls methods to determine the prefix and postfix expression for the tree. Also calculates value of the expressions.

focusGained

public void focusGained(java.awt.event.FocusEvent e)

Used to select all the text whenever the JTextField gets the focus

Specified by:

focusGained in interface java.awt.event.FocusListener

Parameters:

e - - a Focus event

focusLost

public void focusLost(java.awt.event.FocusEvent e)

Required to implement FocusListener but does not do anything.

Specified by:

focusLost in interface java.awt.event.FocusListener

Parameters:

e - - a Focus event

actionPerformed

public void actionPerformed(java.awt.event.ActionEvent e)

Used to process help and exit buttons

Specified by:

actionPerformed in interface java.awt.event.ActionListener

Parameters:

e - - The action event