Java后缀计算器中的StackOverFlowError [英] StackOverFlowError in Java postfix calculator
问题描述
另一个程序正在使用以下类。访问它时，将引发StackOverFlowError。这是我在大学里必须做的一个Postfix计算器的一部分。
The following class is used by another program. When it is accessed, it throws a StackOverFlowError. This is part of a Postfix Calculator I have to do as a project at my university.
任何帮助将不胜感激，谢谢您。我是Java的新手，不知道该怎么做。
Any help would be greatly appreciated, thank you in advance. I'm quite new at Java and I have no idea what to do.
代码：
import java.util.Queue;
import java.util.Stack;
public class MyPostfixMachine implements PostfixMachineInterface {
MyMathOperations mmo = new MyMathOperations();
MyPostfixMachine mpm = new MyPostfixMachine();
public String evaluate(Queue q) {
if (q.isEmpty()) {//if the input is empty, terminate the program
System.exit(0);
}
if (q.size() == 1) {//if there is only one number in the queue, return it as the solution
if (mpm.isParsableToDouble(String.valueOf(q.remove()))) {
return String.valueOf(q.remove());
}
}
Stack<String> finalxp = new Stack<String>();//create an empty stack
if (mpm.isParsableToDouble(String.valueOf(q.remove()))) {//if first element of queue q is a number,push it into the stack
finalxp.push(String.valueOf(q.remove()));
} else {//depending on the operator perform the corresponding operations
if (q.remove() == "+") {
String str = String.valueOf(finalxp.pop());
String str2 = String.valueOf(finalxp.pop());
finalxp.push(mmo.addition(str, str2));
}
if (q.remove() == "-") {
String str = String.valueOf(finalxp.pop());
String str2 = String.valueOf(finalxp.pop());
finalxp.push(mmo.substraction(str, str2));
}
if (q.remove() == "*") {
String str = String.valueOf(finalxp.pop());
String str2 = String.valueOf(finalxp.pop());
finalxp.push(mmo.product(str, str2));
}
if (q.remove() == "/") {
String str = String.valueOf(finalxp.pop());
String str2 = String.valueOf(finalxp.pop());
finalxp.push(mmo.division(str, str2));
}
if (q.remove() == "fibo") {
String str = String.valueOf(finalxp.pop());
finalxp.push(mmo.fibonacci(str));
}
if (q.remove() == "fac") {
String str = String.valueOf(finalxp.pop());
finalxp.push(mmo.factorial(str));
}
if (q.remove() == "han") {
String str = String.valueOf(finalxp.pop());
finalxp.push(mmo.hanoi(str));
}
}
return String.valueOf(finalxp.pop());
}
public boolean isParsableToDouble(String candidate) {
try {
Double.parseDouble(candidate);
return true;
} catch (NumberFormatException nfe) {
return false;
}
}
}
public class MyMathOperations implements MathOperationsInterface {
public String addition(String s1, String s2) {
double A = Double.parseDouble(s1);
double B = Double.parseDouble(s2);
return String.valueOf((A + B));
}
public String substraction(String s1, String s2) {
double A = Double.parseDouble(s1);
double B = Double.parseDouble(s2);
return String.valueOf((A - B));
}
public String product(String s1, String s2) {
double A = Double.parseDouble(s1);
double B = Double.parseDouble(s2);
return String.valueOf((A * B));
}
public String division(String s1, String s2) {
double A = Double.parseDouble(s1);
double B = Double.parseDouble(s2);
return String.valueOf((A / B));
}
public String fibonacci(String s) {
int n = Integer.parseInt(s);
return String.valueOf(fibo(n));
}
public int fibo(int f) {
if (f < 0) {
throw new IllegalArgumentException("Cannot apply Fibonacci method");
} else if (f == 0) {
return 0;
} else if (f == 1) {
return 1;
} else {
return fibo(f - 1) + fibo(f - 2);
}
}
public String hanoi(String s) {
int a = Integer.parseInt(s);
int han = 0;
if (a < 0) {
throw new IllegalArgumentException("Not a valid integer");
} else {
han = (int) Math.pow(2, a) - 1;
}
return String.valueOf(han);
}
public String factorial(String s) {
int a = Integer.parseInt(s);
if (a < 0) {
throw new IllegalArgumentException("Incorrect argument for factorial operatiion");
}
switch (a) {
case 0:
case 1:
return String.valueOf(1);
default:
int res = a;
while (true) {
if (a == 1) {
break;
}
res *= --a;
}
return String.valueOf(res);
}
}
private static double pDouble(String s) {
double res = 0d;
try {
res = Double.parseDouble(s);
} catch (NumberFormatException e) {
System.exit(1);
}
return res;
}
}
推荐答案
问题是您的类MyPostfixMachine 有一个私有字段 MyPostfixMachine mpm ，该字段用新的MyPostfixMachine 初始化了>。由于此新的MyPostfixMachine还具有一个私有字段MyPostfixMachine mpm，该字段已使用新的MyPostfixMachine进行了初始化……您会得到它。 ：）这种情况一直持续下去（或直到堆栈已满）。
The problem is that your class MyPostfixMachine has a private field MyPostfixMachine mpm which is initialized with a new MyPostfixMachine. Since this new MyPostfixMachine also has a private field MyPostfixMachine mpm which is initialized with a new MyPostfixMachine... you get it. :) This goes on and on forever (or until your stack is full).
这是有问题的代码段：
public class MyPostfixMachine implements PostfixMachineInterface {
MyMathOperations mmo = new MyMathOperations();
MyPostfixMachine mpm = new MyPostfixMachine(); // problem is here
// ...
}
<我认为您可以简单地删除私有字段mpm。只需在当前实例上调用方法即可。因此，而不是：
I think you can simply remove the private field mpm. Just call the methods on the current instance. So instead of:
if (mpm.isParsableToDouble(String.valueOf(q.remove()))) {...}
您可以简单地写：
if (isParsableToDouble(String.valueOf(q.remove()))) {...}
或（等价但更明确）：
if (this.isParsableToDouble(String.valueOf(q.remove()))) {...}
无论如何，只需删除私有字段mpm和StackOverflowException应该消失了。
Anyway, just remove the private field mpm and the StackOverflowException should be gone.
这篇关于Java后缀计算器中的StackOverFlowError的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
