Java.lang.NoSuchMethod: main - Help pls

Question

This is the code i got off a book but it seems like it's not working. I got an error which says 'java.lang.NoSuchMethod: main' Help pls...
import java.io.*;
import java.util.*;
class PostfixInterpreter {
     private String postfixString, outputString;
private boolean isOperator(char c) {
     return (c == '+' || c == '-' || c == '*' || c == '/' || c == '^' );
private boolean isSpace(char c) {
     return (c == ' ');
}//end isSpace
public void interpretPostfix() {
     Stack evalStack= new Stack();
     double leftOperand, rightOperand;
     char c;
     StringTokenizer parser = new StringTokenizer(postfixString,"+-*/^ ", true);
     while (parser.hasMoreTokens()){
          String token = parser.nextToken();
          c = token.charAt(0);
          if ((token.length() == 1) && isOperator(c)) {
               rightOperand = ((Double)evalStack.pop()).doubleValue();
               leftOperand = ((Double)evalStack.pop()).doubleValue();
               switch (c) {
                    case'+': evalStack.push(new Double(leftOperand+rightOperand));
                                   break;
                    case'-': evalStack.push(new Double(leftOperand-rightOperand));
                                   break;
                    case'*': evalStack.push(new Double(leftOperand*rightOperand));
                                   break;
                    case'/': evalStack.push(new Double(leftOperand/rightOperand));
                                   break;
                    case'^': evalStack.push(new Double(Math.exp(Math.log(leftOperand)*rightOperand)));
                                   break;
                    default:
                                   break;
               }//end of switch
          }else if((token.length() == 1)&& isSpace(c)){
          }else {
               evalStack.push(Double.valueOf(token));
          }//end if
     }//end while
// remove final result from stack and output it
output("value of postfix expression = " + evalStack.pop());
}//end interpretPostfix
private void output(String input){
     postfixString = input;
     }//end setInput
public String getOutput(){
     return outputString;
}//end getOutput
}//end class PostfixInterpreter
/*Stack class*/
class Stack {
     private int count;
     private int capacity;
     private int capacityIncrement;
     private Object[] itemArray;
//the following defines a no-arg constrcutor for Stack objects
public Stack() {
     count = 0;
     capacity = 100;
     capacityIncrement = 5;
     itemArray = new Object[capacity];
     public boolean empty() {
          return (count ==0);
     public void push(Object X) {
          //if the itemArray does not have enough capacity
          //expend the itemArray by the capacity increment
               if(count == capacity) {
                    capacity += capacityIncrement;
                    Object[] tempArray = new Object[capacity];
                    for (int i=0; i<count;i++){
                         tempArray[i] = itemArray;
               itemArray=tempArray;
          //insert the new item X at the end of the current item sequence
          //and increase the stack's count by one
               itemArray[count++]=X;
public Object pop() {
     if(count==0){
          return null;
     }else{
          return itemArray[--count];
}//end of pop()
public Object peek() {
     if (count == 0){
          return null;
     }else{
          return itemArray[count-1];
}//end peek()

Answer 1

First, when posting code in the future, use the code /code tags. Just highlight the code and click the code. button.
The error probably occurred when you tried to launch the class as an application by entering "java PostfixInterpreter" The java application launcher looks for a method in the PostfixInterpreter class whose signature is exactly public static void main(String[] args)(except 'args' can be any legal variable name). Since your PostfixInterpreter class doesn't have this method, you get the error. If you want this class to run, you have to include the method and code inside the method that runs the application.