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(value2value1); } 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; }

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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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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