我一直在试图找出我的代码的错误无济于事。除了评估后缀表达式之外,我应该为中缀翻译器编写一个中缀。我的代码运行,但不幸的是它不会返回正确的值。Postfix评估器不返回正确的结果
我有一个计算器GUI,只要等号被按下,就会调用下面显示的代码。计算器将一个由空格分隔的字符串作为参数传递。然后我在这个空格分隔的字符串上使用String Tokenizer并从那里开始工作。如果有帮助,我可以提供计算器GUI的代码。
我的问题在于计算器提供的答案。例如,如果我输入(5 + 2),计算器将返回2作为答案,如果再次按等号,则返回5作为答案。如果输入(5 * 2)+(3 * 9),则返回9作为答案,如果再次按等号,则返回5作为一个答案。我尝试了多次通过我的代码,但不幸的是我一直无法找到我的错误。任何帮助将不胜感激!
免责声明:我知道关于使用String Tokenizer的附注。我会用别的东西,但那是需求之一。我还没有执行任何错误检查或检查优先级,因为我想确保它能正常工作,假设输入正确并且先不过分复杂。另外,我知道我的代码不会正确地处理像(5 + 2)-1这样的东西,因为在1周围缺少括号。但是再次,它不能用于比这更简单的事情。 。一旦我能用简单的输入工作,我会担心这一点。最后,这确实是一项家庭作业,但请不要以为我完全是为了完成这件事。只是几个指针将不胜感激。
这里是我的代码:
public class ExpressionEvaluator {
Stack<String> myStack = new Stack<>();
Queue<String> myQueue = new Queue<>();
String curToken; //Current token of my tokenized string.
double temp1; //Place holder for first value of the calc section.
double temp2; //Place holder for second value of the calc section.
public String processInput(String s) {
StringTokenizer st = new StringTokenizer(s);
while (st.hasMoreTokens()) {
curToken = st.nextToken();
if (openParenthesis(curToken)) {
myStack.push(curToken);
}
if (closeParenthesis(curToken)) {
do {
myQueue.enqueue(myStack.pop());
} while (!openParenthesis(myStack.peek()));
}
if (isOperator(curToken)) {
while (!myStack.isEmpty() && !openParenthesis(myStack.peek())) {
myQueue.enqueue(myStack.pop());
}
myStack.push(curToken);
}
if (isDouble(curToken)) {
myQueue.enqueue(curToken);
}
}
while (!myStack.isEmpty()) {
myQueue.enqueue(myStack.pop());
}
while (!myQueue.isEmpty()) {
if (isDouble(myQueue.peek())) {
myStack.push(myQueue.dequeue());
}
else if (isOperator(myQueue.peek())) {
temp1 = Double.parseDouble(myStack.pop());
temp2 = Double.parseDouble(myStack.pop());
myStack.push(Double.toString(calc(temp1, temp2)));
}
else {
myQueue.dequeue();
}
}
return myStack.pop();
}
//Private methods used to simplify/clarify some things.
//Checks if input is an operator, returns true if it is
private boolean isOperator(String str) {
if (str == "+") {return true;}
else if (str == "-") {return true;}
else if (str == "*") {return true;}
else if (str == "/") {return true;}
else if (str == "^") {return true;}
else {return false;}
}
//Checks if input is an open parenthesis "(", returns true if it is
private boolean openParenthesis(String str) {
if (str == "(") {return true;}
else {return false;}
}
//Checks if input is a close parenthesis ")", returns true if it is
private boolean closeParenthesis(String str) {
if (str == ")") {return true;}
else {return false;}
}
//Checks if input is a double, returns true if it is
//I actually got this method from Stack Overflow, so thanks!
private boolean isDouble(String str) {
try {
Double.parseDouble(str);
return true;
} catch (NumberFormatException e) {
return false;
}
}
//Method used to actually do the calculations. I have
//a feeling this is where my problem is, but I can't
//think of a way to fix it.
private double calc(double a, double b) {
String op = myQueue.dequeue();
if (op == "+") {return a+b;}
else if (op == "-") {return a-b;}
else if (op == "*") {return a*b;}
else if (op == "/") {return a/b;}
else if (op == "^") {return Math.pow(a, b);}
else {throw new UnknownElementException(null, "ERROR");}
}
}
对不起,我奇怪的压痕。任何帮助将不胜感激!
谢谢,我会看看这个! – kevinivan05 2015-04-05 01:17:17