[英]getting java.lang.OutOfMemory error with my prefix expression evaluator
Below i have the code for evaluating a prefix expression. 下面我有评估前缀表达式的代码。 I first read the expression into inputArray which allows me to read from right to left, then use evaluationArray to do the operations.
我首先将表达式读入inputArray,这使我可以从右到左阅读,然后使用评估数组进行操作。 I get out of memory error on this line: evaluationStack.push(number);
我在此行出现内存不足错误:EvaluationStack.push(number); I have no idea why this is happening.
我不知道为什么会这样。 any help would be greatly appreciated.
任何帮助将不胜感激。
import java.util.*; 导入java.util。*;
public class PrefixEvaluator
{
//evaluates a prefix expression
public static int evaluate(String input)
{
int number, leftOperand, rightOperand, result;
char operator;
String inputToken = null;
//create input stack
Stack<String> inputStack = new Stack<String>();
//create an integer stack
Stack<Integer> evaluationStack = new Stack<Integer>();
//create string tokenizer containing input string
StringTokenizer tokenizer = new StringTokenizer(input);
//read string into a stack
while (tokenizer.hasMoreTokens())
{
inputToken = tokenizer.nextToken(); //get next token
inputStack.push(inputToken); //push token
}
while (inputStack.isEmpty() != true)
{
//System.out.println(inputStack.pop());
if (isNumber(inputToken))
{
number = Integer.parseInt(inputToken);
evaluationStack.push(number);
}
else //if token is operator
{
operator = inputToken.charAt(0); //get operator
rightOperand = evaluationStack.pop();
leftOperand = evaluationStack.pop();
result = evaluation(operator, leftOperand, rightOperand);
evaluationStack.push(result);
}
}
return evaluationStack.pop();
}
//tests whether token is a number
private static boolean isNumber(String token)
{
char first = token.charAt(0);
if (Character.isDigit(first))
return true;
else
return false;
}
//perform an operation on two operands
private static int evaluation(char operator, int leftOperand, int rightOperand)
{
if (operator == '+')
return leftOperand + rightOperand;
else if (operator == '-')
return leftOperand - rightOperand;
else if (operator == '*')
return leftOperand * rightOperand;
else if (operator == '%')
return leftOperand % rightOperand;
else
return leftOperand / rightOperand;
}
public static void main (String [] args)
{
evaluate("* 4 - 165 235");
}
}
If you step through your code in your debugger you will see that this code is an infinite loop. 如果在调试器中逐步执行代码,您将看到此代码是一个无限循环。
while (inputStack.isEmpty() != true)
{
//System.out.println(inputStack.pop());
if (isNumber(inputToken))
{
number = Integer.parseInt(inputToken);
evaluationStack.push(number);
You keep testing inputToken and adding it to a stack but you never change it so it runs until you run out of memory. 您一直在测试inputToken并将其添加到堆栈中,但是您从不对其进行更改,因此它将一直运行到内存用完为止。
Perhaps you intended to have this at the start of the loop 也许您打算在循环开始时使用它
inputToken = inputStack.pop();
If you also add 如果您还添加
System.out.println(evaluate("* 4 - 165 235"));
it prints 它打印
280
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