Stacks and Queues - Advanced Topics in Java: Core Concepts in Data Structures - page 127

Using this definition of NodeData , Program P4.5 will work fine if we simply replace all occurrences of getData
with getCharData .
The function eval , which evaluates an expression given its postfix form, is shown as part of Program P4.6. We test
eval by placing the following as the last statement in main :
System.out.printf("\nIts value is %d\n", eval(post, n));
The classes Node and Stack are not shown in Program P4.6. The class Node is the same as that in Program P4.3.
The class Stack is the same as that in Program P4.3 with the addition of peek() .
Program P4.6
import java.io.*;
public class EvalExpression {
public static void main(String[] args) throws IOException {
char[] post = new char[255];
int n = readConvert(post);
printPostfix(post, n);
System.out.printf("\nIts value is %d\n", eval(post, n));
} //end main
public static int readConvert(char[] post) throws IOException {
//Read the expression and convert to postfix. Return the size of postfix.
Stack S = new Stack();
int h = 0;
char c;
System.out.printf("Type an infix expression and press Enter\n");
char token = getToken();
while (token != '\0') {
if (Character.isDigit(token)) post[h++] = token;
else if (token == '(') S.push(new NodeData('('));
else if (token == ')')
while ((c = S.pop().getCharData()) != '(') post[h++] = c;
else {
while (!S.empty() &&
precedence(S.peek().getCharData()) >= precedence(token))
post[h++] = S.pop().getCharData();
S.push(new NodeData(token));
}
token = getToken();
}
while (!S.empty()) post[h++] = S.pop().getCharData();
return h;
} //end readConvert
public static void printPostfix(char[] post, int n) {
System.out.printf("\nThe postfix form is \n");
for (int h = 0; h < n; h++) System.out.printf("%c ", post[h]);
System.out.printf("\n");
} //end printPostfix