I am writing an evaluation code for polish notation. When I overcome ClassCastException I get EmptyStack and when I solve Emptystack I get ClassCast I'm in a loop. Here is how I wanted to evaluate the Polish notation:
First I get a string from the user then put it into a stack. For evaluating I use a second stack. Why? Because: An example string: "* + * + 1 2 + 3 4 5 6" First operation here is to add up 3 and 4 but what I'm gonna do with 5 and 6? I put them in another stack. Let's say stack2. I start popping until I found an operator, in this condition I pushed 6 5 4 3 into stack2 and found a plus operator. Then I pop 2 numbers which I pushed to stack2 (the top 2 numbers are 3 and 4), add them up, and push them to stack again. I should evaluate but seems like I am missing a point or this wasn't a good idea at first. Here is my code:
public class Main {
public static void stack(String srt){ // this function puts the string in srt stack
String arr[] = srt.split(" "); // I am recognizing if there is a 2 or more digit number
int size= arr.length; // with receiving prefix with " " btw every number and operator
Stack stack= new Stack();
for (String s : arr) {
// System.out.println(s);
stack.push(s);
}
// for (int i = 0; i < size; i++) {
// System.out.println(stack.pop()); // I checked to see if any
// problems first now I dont start this
// }
evaluate(stack); // then calls the evaluate function
}
public static void evaluate(Stack stack){
Stack stack2= new Stack();
stack2.push(stack.pop());// cuz of there cant be an operator there I pop first 2 number
stack2.push(stack.pop());
for (int i = 0; i < (stack.capacity()*2); i++) { // I had a hard time calculating how many times
// I should cycle through this for and leave it 2 times as stack capacity
if(stack.peek().toString().equals("*") || stack.peek().toString().equals("-") || stack.peek().toString().equals("/") || stack.peek().toString().equals("+")){
System.out.println("Checkpoint1");
// System.out.println(stack2.peek());
int s2= Integer.parseInt((String) stack2.pop());
int s1= Integer.parseInt((String) stack2.pop());
double s3;
String c = (String) stack.pop();
switch (c) {
case "+":
s3=s1+s2;
stack2.push(s3);
case "-":
s3=s1-s2;
stack2.push(s3);
case "*":
s3=s1*s2;
stack2.push(s3);
case "/":
s3=s1/s2;
stack2.push(s3);
}
}else{
System.out.println("Checkpoint 2");
stack2.push(Integer.parseInt((String) stack.pop()));
// System.out.println(stack.peek());
}
}
// System.out.println(stack.peek());
// System.out.println(stack2.peek());
}
public static void main(String[] args) {
String examplestr ="* + * + 1 2 + 3 4 5 6";
stack(examplestr);
}
}
Thank you for your help!!!
So turns out the switch-case doesn't operate correctly because I forgot a fundamental part "break". For EmptyStackException, I made a try-catch and put them inside so when it returns empty stack I know evaluation is done and print the result. BUT I still don't know how to deal with these little problems. It feels like I did not solve them properly. Gotta work more. Thanks.
Edit: I made some more adjustments and this is my final working code. I couldn't detect an error in the results yet.
Here is the working code;
import java.util.EmptyStackException;
import java.util.Stack;
public class Main2 {
public static void stack(String srt) {
String arr[] = srt.split(" ");
int size = arr.length;
Stack stack = new Stack();
for (int i = 0; i < size; i++) {
if (arr[i].toString().equals("*") || arr[i].toString().equals("-") || arr[i].toString().equals("/") || arr[i].toString().equals("+"))
stack.push(arr[i]);
else
stack.push(Double.parseDouble(arr[i]));
}
// for (int i = 0; i < size; i++) {
// System.out.println(stack.pop());
// }
evaluate(stack);
}
public static void evaluate(Stack stack) {
Stack stack1 = new Stack();
stack1.push(stack.pop());
stack1.push(stack.pop());
for (int i = 0; i < stack1.capacity(); i++) {
try {
if (stack.peek().toString().equals("*") || stack.peek().toString().equals("-") || stack.peek().toString().equals("/") || stack.peek().toString().equals("+")) {
// System.out.println("Checkpoint1");
double s1 = (double) stack1.pop();
double s2 = (double) stack1.pop();
double s3;
String operator = String.valueOf(stack.pop());
switch (operator) {
case "+":
s3 = s1 + s2;
stack1.push(s3);
break;
case "-":
s3 = s1 - s2;
stack1.push(s3);
break;
case "*":
s3 = s1 * s2;
stack1.push(s3);
break;
case "/":
s3 = s1 / s2;
stack1.push(s3);
break;
}
} else {
// System.out.println("Checkpoint 2");
stack1.push(Double.parseDouble(String.valueOf(stack.pop())));
}
} catch (EmptyStackException e) {
System.out.println("Notasyonun sonucu: " + stack1.peek());
}
}
}
public static void main(String[] args) {
String notasyon = scanner.nextLine();
stack(notasyon);
}
}