The programming project involves writing a program that parses, using recursive
ID: 3556901 • Letter: T
Question
The programming project involves writing a program that parses, using recursive descent, a GUI definition language defined in an input file and generates the GUI that it defines. The grammar for this language is defined below:
gui ::=
Window STRING '(' NUMBER ',' NUMBER ')' layout widgets End '.'
layout ::=
Layout layout_type ':'
layout_type ::=
Flow |
Grid '(' NUMBER ',' NUMBER [',' NUMBER ',' NUMBER] ')'
widgets ::=
widget widgets |
widget
widget ::=
Button STRING ';' |
Group radio_buttons End ';' |
Label STRING ';' |
Panel layout widgets End ';' |
Textfield NUMBER ';'
radio_buttons ::=
radio_button radio_buttons |
radio_button
radio_button ::=
Radio STRING ';'
In the above grammar, the red symbols are nonterminals, the blue symbols are tokens and the black punctuation symbols are BNF metasymbols. Among the tokens those in title case are keywords. The character literals are punctuation tokens.
Below is an explanation of the meaning of some of the symbols in the above productions that should help you understand the actions that are to be performed when each of the productions is parsed:
You parser should properly handle the fact that panels can be nested in other panels. Recursive productions must be implemented using recursion. Syntactically incorrect input files should detect and report the first error.
Below is an example of an input file:
Window "Calculator" (200, 200) Layout Flow:
Textfield 20;
Panel Layout Grid(4, 3, 5, 5):
Button "7";
Button "8";
Button "9";
Button "4";
Button "5";
Button "6";
Button "1";
Button "2";
Button "3";
Label "";
Button "0";
End;
End.
The above input file should produce the GUI shown below:
Explanation / Answer
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Calculator implements ActionListener{
char o;
int ctr=0;
String value="", cv="", oBtn;
Double answer, v1, v2;
Double NumberConverted;
Frame f;
Panel p1, p2, p3, p4, p5, p6;
private TextField tField;
private Menu EditMenu;
private MenuBar menuBar;
private MenuItem fmi1, fmi2, fmi3;
private Button num0, num1, num2, num3, num4, num5, num6, num7, num8,
num9;
private Button bAdd, bSub, bMul, bDiv, bPer, bSqrt, bFrac, bInt, bDot,
bCE, equals, backspace, clear;
Calculator(){
f = new Frame("Calculator");
menuBar = new MenuBar();
EditMenu = new Menu ("Edit");
fmi1 = new MenuItem(" Copy ");
fmi2 = new MenuItem(" Paste ");
fmi3 = new MenuItem(" Quit ");
EditMenu.add(fmi1);
EditMenu.add(fmi2);
EditMenu.addSeparator();
EditMenu.add(fmi3);
p1 = new Panel();
p2 = new Panel();
p3 = new Panel();
p4 = new Panel();
p5 = new Panel();
p6 = new Panel();
tField = new TextField(35);
num0 = new Button ("0");
num1 = new Button ("1");
num2 = new Button ("2");
num3 = new Button ("3");
num4 = new Button ("4");
num5 = new Button ("5");
num6 = new Button ("6");
num7 = new Button ("7");
num8 = new Button ("8");
num9 = new Button ("9");
bAdd = new Button ("+");
bSub = new Button ("-");
bMul = new Button ("x");
bDiv = new Button ("/");
bPer = new Button ("%");
bSqrt = new Button ("sqrt");
bFrac = new Button ("1/x");
bInt = new Button ("+/-");
bDot = new Button (".");
bCE = new Button ("CE");
equals = new Button ("=");
backspace = new Button ("Backspace");
clear = new Button ("C");
}
public void launchFrame(){
tField.setText("0.");
tField.setEnabled(false);
menuBar.add(EditMenu);
p2.add(backspace);
p2.add(bCE);
p2.add(clear);
p3.add(num7);
p3.add(num8);
p3.add(num9);
p3.add(bDiv);
p3.add(bSqrt);
p4.add(num4);
p4.add(num5);
p4.add(num6);
p4.add(bMul);
p4.add(bPer);
p5.add(num1);
p5.add(num2);
p5.add(num3);
p5.add(bSub);
p5.add(bFrac);
p6.add(num0);
p6.add(bInt);
p6.add(bDot);
p6.add(bAdd);
p6.add(equals);
p2.setLayout(new GridLayout (1, 3, 2, 2) );
p3.setLayout(new GridLayout (1, 3, 2, 2) );
p4.setLayout(new GridLayout (1, 3, 2, 2) );
p5.setLayout(new GridLayout (1, 3, 2, 2) );
p6.setLayout(new GridLayout (1, 3, 2, 2) );
f.setLayout(new GridLayout (6, 1) );
f.setResizable(false);
f.setSize(300,250);
f.add(tField);
f.add(p2);
f.add(p3);
f.add(p4);
f.add(p5);
f.add(p6);
f.setVisible(true);
f.setMenuBar(menuBar);
f.pack();
// ACTION LISTENERS
clear.addActionListener(this);
bCE.addActionListener(this);
num0.addActionListener(this);
num1.addActionListener(this);
num2.addActionListener(this);
num3.addActionListener(this);
num4.addActionListener(this);
num5.addActionListener(this);
num6.addActionListener(this);
num7.addActionListener(this);
num8.addActionListener(this);
num9.addActionListener(this);
bAdd.addActionListener(this);
bSub.addActionListener(this);
bMul.addActionListener(this);
bDiv.addActionListener(this);
bPer.addActionListener(this);
bInt.addActionListener(this);
bSqrt.addActionListener(this);
bFrac.addActionListener(this);
bDot.addActionListener(this);
equals.addActionListener(this);
backspace.addActionListener(this);
fmi1.addActionListener(this);
fmi2.addActionListener(this);
fmi3.addActionListener(this);
}
/* |------------ START OF ACTION EVENTS ------------| */
public void actionPerformed(ActionEvent a){
try{
/* |-------- Handling Exceptions ---------| */
if(a.getSource()==num0){
value+=0;
tField.setText(value);
}
if(a.getSource()==num1){
value+=1;
tField.setText(value);
}
if(a.getSource()==num2){
value+=2;
tField.setText(value);
}
if(a.getSource()==num3){
value+=3;
tField.setText(value);
}
if(a.getSource()==num4){
value+=4;
tField.setText(value);
}
if(a.getSource()==num5){
value+=5;
tField.setText(value);
}
if(a.getSource()==num6){
value+=6;
tField.setText(value);
}
if(a.getSource()==num7){
value+=7;
tField.setText(value);
}
if(a.getSource()==num8){
value+=8;
tField.setText(value);
}
if(a.getSource()==num9){
value+=9;
tField.setText(value);
}
if (a.getSource() == bAdd){
v1 = Double.parseDouble( tField.getText() );
ctr=0;
o = '+';
value="";
tField.setText("" +value);
}
if (a.getSource() == bSub){
v1 = Double.parseDouble( tField.getText() );
ctr=0;
o = '-';
value="";
tField.setText("" +value);
}
if (a.getSource() == bMul){
v1 = Double.parseDouble( tField.getText() );
ctr=0;
o = 'x';
value="";
tField.setText("" +value);
}
if (a.getSource() == bDiv){
v1 = Double.parseDouble( tField.getText() );
ctr=0;
o = '/';
value="";
tField.setText("" +value);
}
if (a.getSource() == bPer){
v1 = Double.parseDouble( tField.getText() );
ctr=0;
value="";
answer = (v1/100);
tField.setText("" +answer);
}
/* |-- EQUALS ACTION --| */
if(a.getSource()==equals){
value="";
v2 = Double.parseDouble(tField.getText());
if(o=='+'){
ctr=0;
answer = v1 + v2;
tField.setText("" +answer);
value=""; v1=null; v2=null;
}
else if(o=='-'){
ctr=0;
answer = v1 - v2;
tField.setText("" +answer);
value=""; v1=null; v2=null;
}
else if(o=='x'){
ctr=0;
answer = v1 * v2;
tField.setText("" +answer);
value=""; v1=null; v2=null;
}
else if(o=='/'){
ctr=0;
answer = v1 / v2;
tField.setText("" +answer);
value=""; v1=null; v2=null;
}
else if(o=='%'){
ctr=0;
answer = v1 % v2;
tField.setText("" +answer);
value=""; v1=null; v2=null;
}
else{}
}
/* |-- EQUALS ACTION --| */
/* |-- Clear --| */
if(a.getSource()==clear){
ctr=0;
v1=null;
v2=null;
value="";
answer=0.;
tField.setText("0.");
}
if(a.getSource()==bCE){
ctr=0;
value="";
tField.setText("0.");
}
/* |-- Point --| */
if(a.getSource() == bDot){
if(ctr==0){
value+=".";
ctr+=1;
tField.setText("" +value);
}
else{
System.out.print("");
}
}
/* |-- Back Space --| */
if(a.getSource() == backspace){
value = value.substring(0, value.length()-1 );
tField.setText("" +value);
}
/* |-- Square Root --| */
if(a.getSource() == bSqrt){
ctr=0;
value = "";
v1 = Math.sqrt( Double.parseDouble( tField.getText() ) );
tField.setText("" +v1);
}
/* |-- Integer --| */
if(a.getSource() == bInt){
ctr=0;
NumberConverted = ( Double.parseDouble(tField.getText()) * -1 );
value = "";
tField.setText("" +NumberConverted);
}
/* |-- Reciprocal --| */
if(a.getSource() == bFrac){
ctr=0;
value = "";
Double NumberContainer = ( 1 / Double.parseDouble(
tField.getText() ) );
tField.setText("" +NumberContainer);
}
// ------------ Menu Item Actions ------------ //
if(a.getSource() == fmi1){
cv = tField.getText();
}
if(a.getSource() == fmi2){
tField.setText("" +cv);
}
if(a.getSource() == fmi3){
System.exit(0);
}
} // End of Try
/* |-------- Attempting To Catch Runtime Errors ---------| */
catch(StringIndexOutOfBoundsException str){}
catch(NumberFormatException nfe){}
catch(NullPointerException npe){}
} // END OF ACTION EVENTS
public static void main (String args[]){
Calculator s = new Calculator();
s.launchFrame();
}
}
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