class Arithmetic {
public static Lexer lex = new Lexer ("(5+2)*3)");
public static void main (String [] args) {
}
public static class Lexer {
static int i;
static int j;
static String lexstream;
static char ch;
Lexer (String lexstream) {
this.lexstream = lexstream;
i = 0;
j = 0;
}
public static char getnext () {
if ((lexstream.charAt (i) == ' ') || (lexstream.charAt (i) == '\t') || (lexstream.charAt (i) == '\n') || (lexstream.charAt (i) == '\r'))
while ((lexstream.charAt (i) == ' ') || (lexstream.charAt (i) == '\t') || (lexstream.charAt (i) == '\n') || (lexstream.charAt (i) == '\r'))
i++;
if (lexstream.charAt (i) == '(') {
j = 1;
i++;
ch = '(';
}
else if (lexstream.charAt (i) == ')') {
j = 1;
i++;
ch = ')';
}
else if (lexstream.charAt (i) == '*') {
j = 1;
i++;
ch = '*';
}
else if (lexstream.charAt (i) == '+') {
j = 1;
i++;
ch = '+';
}
else if ((lexstream.charAt (i) >= '0') && (lexstream.charAt (i) <= '9')) {
ch = lexstream.charAt (i);
j = 1;
i++;
}
else {
System.out.println ("error");
System.exit (2);
}
return ch;
}
public static void undo () {
i = i-j;
j = 0;
}
}
/* Syntaxregeln
expr ::= term expr2
expr2 ::= '+' term expr2 | e
term ::= fact term2
term2 ::= '*' fact term2 | e
fact ::= const | '(' expr ')'
*/
public class Syntaxtree {
public Syntaxtree left;
public Syntaxtree right;
public char value;
public static int getval () {
System.out.println (this.value);
if (this.left != null)
this.left.getval ();
if (this.right != null)
this.right.getval ();
}
}
public static class Expr extends Syntaxtree {
Expr () {
this.right = new Term ();
this.left = new Expr2 ();
this.value = '+';
}
}
public static class Expr2 extends Syntaxtree {
Expr2 () {
if (lex.getnext () == '+') {
this.right = new Term ();
this.left = new Expr2 ();
this.value = '+';
}
else {
lex.undo ();
this.right = null;
this.left = null;
this.value = '0';
}
}
}
public static class Term extends Syntaxtree {
Term () {
char ch;
ch = lex.getnext ();
if (ch == '(') {
this.right = new Expr ();
if ((ch = lex.getnext ()) != ')') {
System.out.println ("Error");
System.exit(1);
}
this.left = new Term2 ();
this.value = '*';
}
else {
lex.undo ();
this.right = new Fact ();
this.left = new Term2 ();
this.value = '*';
}
}
}
public static class Term2 extends Syntaxtree {
public static char ch;
Term2 () {
if ((lex.getnext ()) == '*') {
if ((ch = lex.getnext ()) == '(') {
this.right = new Expr ();
if ((ch = lex.getnext ()) != ')') {
System.out.println ("error");
System.exit (1);
}
this.right = new Term2 ();
this.value = '*';
}
else {
lex.undo ();
this.right = new Fact ();
this.left = new Term2 ();
this.value = '*';
}
}
else {
lex.undo ();
this.right = null;
this.left = null;
this.value = '1';
}
}
}
public static class Fact extends Syntaxtree {
public char ch;
Fact () {
if (((ch = lex.getnext ()) >= '0') && (lex.getnext () <= '9')) {
this.value = ch;
this.right = null;
this.left = null;
}
}
}
}
