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help with a second infix to postfix and reversing infix to postfix
ok, I have a program that uses a list and stack to convert Infix to Postfix. I finally worked out all the kinks with it except one thing, which I'll get into in a minute, and now I want to reverse the process, turn Postfix into Infix. I gave it a go, and the output was all wrong. I tried debugging it and I have no idea where it's messing up. So I have 2 problems
1)If I make a MyTest class like:
public class MyTest{
public static void main(String args[]){
Postfix px = new Postfix();
String input = "(a1+a2*a123)+123";
px.parsing(input);
px.conversion();
px.clear();
input = "a*b+c*d*e+f";
px.parsing(input);
px.conversion();
px.clear();
}
}
It will output the first part correctly, but when it gets to the second input it throws:
java.lang.StringIndexOutOfBoundsException
right after running the parsing method, which I don't understand why it would do that.
2) When I run the MyTest class without the second input but with the reverse method in there it prints out a weird output that looks like this:
( a123 + ) )( ( ( + a1 ) * a2 )( ( a1 + ( a2 * a123 ) ) + 123 ) when it should be
( ( a1 + ( a2 * a123 ) ) + 123 )
I walked through the debug and I don't see how it could be doing this because it looked ok to me, but then again I am also new to debugging.
I'll put up the code to my Postfix class below. Any help you guys could offer would be greatly appreciated.
<pre><code>class Postfix {
private ListReferenceBaseCSCE1040 token = new ListReferenceBaseCSCE1040();
private String output;
private StackReferenceBaseCSCE1040 aStack = new StackReferenceBaseCSCE1040();
public Postfix(){
token = new ListReferenceBaseCSCE1040();
aStack = new StackReferenceBaseCSCE1040();
output = "";
}//end constructor postfix
//this takes token and converts it to postfix
public void conversion(){
for(int i = 1; i <= token.size(); i++){
if( token.get(i).equals("(")){
aStack.push(token.get(i));
}else if(token.get(i).equals(")")){
while(!aStack.peek().equals("(")){
output = output + " " + aStack.pop() + " ";
} //end while
aStack.pop(); // to pop the ( so it doesn't get printed later
}else if((token.get(i).equals("*")) || (token.get(i).equals("/")) || (token.get(i).equals("+")) || (token.get(i).equals("-"))){
while(!aStack.isEmpty() && precedence(token.get(i)) <= precedence(aStack.peek())){
output = (output + " " + aStack.pop());
} //end while
aStack.push(token.get(i));
}else{
output += token.get(i) + " ";
} //end ifs
} //end for
while(!aStack.isEmpty()){
output = output + aStack.pop();
} // end while
System.out.println("Output: " + output);
System.out.println("");
} //end conversion
// sets the precedence of the operators
public int precedence(Object op){
if((op.equals("*")) || (op.equals("/"))){
return 2;
}else if((op.equals("+")) || (op.equals("-"))){
return 1;
}else{ //parenthesis
return 0;
} //end ifs
} //end precedence
public void parsing(String input){
String aToken = "";
int numToken = 0;
int x = 0;
if(output == ""){
System.out.println("Infix to Postfix");
}
while( x < input.length() ){
if((input.charAt(x) == '(') || (input.charAt(x) == ')') || (input.charAt(x) == '*') || (input.charAt(x) == '/') || (input.charAt(x) == '+') || (input.charAt(x) == '-')){
aToken = aToken + input.charAt(x);
numToken++;
token.add(numToken, aToken);
aToken = "";
}else if(Character.isLetter(input.charAt(x))){
aToken += input.charAt(x);
while((x+1<input.length()) && (Character.isLetter(input.charAt(x+1))) || (Character.isDigit(input.charAt(x+1)))){
x++;
aToken += input.charAt(x);
} //end while
numToken++;
token.add(numToken, aToken);
aToken = "";
}else if(Character.isDigit(input.charAt(x))){
aToken += input.charAt(x);
while((x+1 < input.length()) && (Character.isDigit(input.charAt(x+1)))){
x++;
aToken += input.charAt(x);
} // end while
numToken++;
token.add(numToken, aToken);
aToken = "";
}
x++; //adds to the main while loop
} // end while
System.out.println("Input: " + input);
} // end parsing
public void clear(){
token = new ListReferenceBaseCSCE1040();
aStack = new StackReferenceBaseCSCE1040();
output = "";
}//end clear
//THIS IS WHERE THINGS GET WEIRD********************************************
public void reverse(){
String tempout = "";
Object operand1 = "";
Object operand2 = "";
System.out.println("Postfix to Infix");
this.parsing(output);
for(int i = 1; i < token.size(); i++){
if(token.get(i).equals("*") || token.get(i).equals("/") || token.get(i).equals("+") || token.get(i).equals("-")){
operand2 = aStack.pop();
operand1 = aStack.pop();
tempout = ("( " + operand1 + " " + token.get(i)+ " " + operand2 + " )");
aStack.push(tempout);
tempout = "";
}else{
aStack.push(token.get(i));
}//end ifs
}//end for
while(!aStack.isEmpty()){
tempout = tempout + aStack.pop();
}
System.out.println("Output: " + tempout);
}//end reverse
}//end postfix</code></pre>
scratch the second problem. I fixed my reverse method. Main problem was a forgotten <= in the for loop. I still can't figure out why its throwing that exception though so any help with that would be great.
You
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