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Infix to Postfix conversion using java .
import java.util.*;
public class itof{
private static final char ADD = '+', SUBTRACT = '-';
private static final char MULTIPLY = '*', DIVIDE = '/';
private static final char POWER ='^';
public itof(){
}
// Private methods:
private boolean isOperator(char c) { // Tell whether c is an operator.
return c == '+' || c == '-' || c == '*' || c == '/' || c == '^'
|| c=='(' || c==')';
}//end isOperator
private boolean isSpace(char c) { // Tell whether c is a space.
return (c == ' ');
}//end isSpace
private boolean lowerPrecedence(char op1, char op2) {
// Tell whether op1 has lower precedence than op2, where op1 is an
// operator on the left and op2 is an operator on the right.
// op1 and op2 are assumed to be operator characters (+,-,*,/,^).
switch (op1) {
case '+':
case '-':
return !(op2=='+' || op2=='-') ;
case '*':
case '/':
return op2=='^' || op2=='(';
case '^':
return op2=='(';
case '(': return true;
default: // (shouldn't happen)
return false;
}
} // end lowerPrecedence
// Method to convert infix to postfix:
public String convertToPostfix(String infix) {
Stack operatorStack = new Stack();
char c;
StringTokenizer parser = new StringTokenizer(infix,"+-*/^() ",true);
StringBuffer postfix = new StringBuffer(infix.length());
while (parser.hasMoreTokens()) {
String token = parser.nextToken();
c = token.charAt(0);
if ( (token.length() == 1) && isOperator(c) ) {
while (!operatorStack.empty() &&
!lowerPrecedence(((String)operatorStack.peek()).charAt(0), c))
postfix.append(" ").append((String)operatorStack.pop());
if (c==')') {
String operator = (String)operatorStack.pop();
while (operator.charAt(0)!='(') {
postfix.append(" ").append(operator);
operator = (String)operatorStack.pop();
}
}
else
operatorStack.push(token);
}
else if ( (token.length() == 1) && isSpace(c) ) {
}
else {
postfix.append(" ").append(token);
}
}
while (!operatorStack.empty())
postfix.append(" ").append((String)operatorStack.pop());
return postfix.toString();
}
public int evaluate(String expr) {
// assert (isValid(expr));
Stack stack = new Stack();
int op1, op2, result = 0;
String token;
StringTokenizer tokenizer = new StringTokenizer(expr);
while (tokenizer.hasMoreTokens()) {
token = tokenizer.nextToken();
char c = token.charAt(0);
if (isOperator(c)) {
op2 = ((Integer) stack.pop()).intValue();
op1 = ((Integer) stack.pop()).intValue();
result = evalSingleOp(token.charAt(0), op1, op2);
stack.push(new Integer(result));
}
else
stack.push(new Integer(Integer.parseInt(token)));
}
result = ((Integer) stack.pop()).intValue();
return result;
}
private int evalSingleOp(char operation, int op1, int op2) {
int result = 0;
switch (operation) {
case ADD :
result = op1 + op2;
break;
case SUBTRACT :
result = op1 - op2;
break;
case MULTIPLY :
result = op1 * op2;
break;
case DIVIDE :
result = op1 / op2;
case POWER :
result = (int) Math.pow(op1,op2);
}
return result;
}
public static void main(String[] args) { // Test method for the class.
String[] testString = {"2*(5+10)"};
itof converter = new itof();
System.out.println("\nTest for convertToPostfix:\n");
for (int i=0; i<testString.length; i++) {
System.out.println("infix: " + testString[i]);
System.out.println("postfix: " + converter.convertToPostfix(testString[i]));
System.out.println("postfix evaluation: " + converter.evaluate( converter.convertToPostfix(testString[i])));
System.out.println();
}
} // end main
}//end class InfixToPostfix
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