Stacks and Queues - Advanced Topics in Java: Core Concepts in Data Structures - page 128

public static char getToken() throws IOException {
int n;
while ((n = System.in.read()) == ' ') ; //read over blanks
if (n == '\r') return '\0';
return (char) n;
} //end getToken
public static int precedence(char c) {
//Returns the precedence of the given operator
if (c == '(') return 0;
if (c == '+' || c == '-') return 3;
if (c == '*' || c == '/') return 5;
return -99; //error
} //end precedence
public static int eval(char[] post, int n) {
//Given the postfix form of an expression, returns its value
int a, b, c;
Stack S = new Stack();
for (int h = 0; h < n; h++) {
if (Character.isDigit(post[h]))
S.push(new NodeData(post[h] - '0'));
else {
b = S.pop().getIntData();
a = S.pop().getIntData();
if (post[h] == '+') c = a + b;
else if (post[h] == '-') c = a - b;
else if (post[h] == '*') c = a * b;
else c = a / b;
S.push(new NodeData(c));
} //end if
} //end for
return S.pop().getIntData();
} //end eval
} //end class EvalExpression
class NodeData {
char ch;
int num;
public NodeData(char c) {
ch = c;
}
public NodeData(int n) {
num = n;
}