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Im trying to figure out a java homework assignment where I have to evaluate postfix expressions using stacks and Stringtokenizer as well as a isNumber method. when I try to run it it gives me an error. this is the code I have so far:   static double evaluatePostfixExpression(String expression){     // Write your code       Stack aStack = new Stack();       double value1, value2;     String token;     StringTokenizer tokenizer = new StringTokenizer(expression);     while (tokenizer.hasMoreTokens()) {       token = tokenizer.nextToken();       if(isNumber(expression)) {         value1 = (double)aStack.pop();         value2 = (double)aStack.pop();         if (token.equals("+")) {           aStack.push(value2+value1);         } else if (token.equals("-")) {           aStack.push(value2-value1);         } else if (token.equals("*")) {           aStack.push(value2*value1);         } else if (token.equals("/")) {           aStack.push(value2/value1);         }       }           }     Object lastValue = aStack.pop();     if (!aStack.isEmpty()) {       System.out.println("Stack has more operands than operators");       return Double.NEGATIVE_INFINITY;     }     else       return (double) lastValue;         //return -1;   }

Im trying to figure out a java homework assignment where I have to evaluate postfix expressions using stacks and Stringtokenizer as well as a isNumber method. when I try to run it it gives me an error. this is the code I have so far:   static double evaluatePostfixExpression(String expression){     // Write your code       Stack aStack = new Stack();       double value1, value2;     String token;     StringTokenizer tokenizer = new StringTokenizer(expression);     while (tokenizer.hasMoreTokens()) {       token = tokenizer.nextToken();       if(isNumber(expression)) {         value1 = (double)aStack.pop();         value2 = (double)aStack.pop();         if (token.equals("+")) {           aStack.push(value2+value1);         } else if (token.equals("-")) {           aStack.push(value2-value1);         } else if (token.equals("*")) {           aStack.push(value2*value1);         } else if (token.equals("/")) {           aStack.push(value2/value1);         }       }           }     Object lastValue = aStack.pop();     if (!aStack.isEmpty()) {       System.out.println("Stack has more operands than operators");       return Double.NEGATIVE_INFINITY;     }     else       return (double) lastValue;         //return -1;   }

C++ Programming: From Problem Analysis to Program Design
C++ Programming: From Problem Analysis to Program Design
8th Edition
ISBN:9781337102087
Author:D. S. Malik
Publisher:D. S. Malik
Chapter18: Stacks And Queues
Section: Chapter Questions
Problem 2SA
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Im trying to figure out a java homework assignment where I have to evaluate postfix expressions using stacks and Stringtokenizer as well as a isNumber method. when I try to run it it gives me an error.

this is the code I have so far:

 

static double evaluatePostfixExpression(String expression){
    // Write your code  
    Stack aStack = new Stack();
 
    double value1, value2;
    String token;
    StringTokenizer tokenizer = new StringTokenizer(expression);
    while (tokenizer.hasMoreTokens()) {
      token = tokenizer.nextToken();
      if(isNumber(expression)) {
        value1 = (double)aStack.pop();
        value2 = (double)aStack.pop();

        if (token.equals("+")) {
          aStack.push(value2+value1);
        } else if (token.equals("-")) {
          aStack.push(value2-value1);
        } else if (token.equals("*")) {
          aStack.push(value2*value1);
        } else if (token.equals("/")) {
          aStack.push(value2/value1);
        }
      }

     
    }
    Object lastValue = aStack.pop();
    if (!aStack.isEmpty()) {
      System.out.println("Stack has more operands than operators");
      return Double.NEGATIVE_INFINITY;
    }
    else
      return (double) lastValue;
   
    //return -1;
  }
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