//************************************************************//  InfixToPostfix.Java      Authors:  Lewis/Chase//  //  Provides an implementation of an infix to postfix//  converter for expressions//************************************************************/**Infix to Postfix Conversion:* Scan the input String using Scanner* While there are more tokens   o If the next token is of length greater than 1, it is a      multiple digit number and is added to the result   o Else if the next token is 1 digit number, it is added      to the result   o Else if the next token is a right parenthesis,      * Pop elements off of the stack, adding them to the         result until the top element of the stack is a matching         left parenthesis      * Pop the left parenthesis off of the stack   o Else if the next token is an operator (+,-,*,/)      * Then compare the token to the top of the stack to         determine precedence      * While the operator on the stack has precedence      * Pop the top element off of the stack and add it to the         result      * Push the current operator on the stack* While there are elements remaining on the stack   o Pop the top element off of the stack and add it to the result* The result is a postfix expression in reverse order so reverse   it and return it*/import jss2.*;import java.util.Scanner; public class InfixToPostfix {  /**********************************************************     Constructor  **********************************************************/  public InfixToPostfix()  {       }  /**********************************************************     Returns a postfix expression of this infix string      as a list.  **********************************************************/  public ArrayUnorderedList convert(String infix)  {    ArrayUnorderedList<String> tokenList =                         new ArrayUnorderedList<String>();    ArrayStack<String> postStack = new ArrayStack<String>();    int toPush=0,operand1=0, operand2=0;    boolean precedence=true;    char tempChar;    String tempToken;    String input;    input = infix;    Scanner s = new Scanner(input);    for(int scan = 0; scan < input.length(); scan++)    {      while(s.hasNext())      {        tempToken = s.next();        tempToken = tempToken.toString();                if(tempToken.length()>1)        {          tokenList.addToFront(tempToken);        }        else if(tempToken.length() ==1)        {          tempChar = tempToken.charAt(0);                    if(tempChar >= '0' && tempChar <= '9')            tokenList.addToFront(tempToken);          else if(tempToken.equals("(") )            postStack.push(tempToken);                     else if(tempToken.equals(")") )          {            while(!postStack.isEmpty() &&                    postStack.peek() != "("  )            {                              tokenList.addToFront(postStack.pop());             }            if (!postStack.isEmpty())              postStack.pop();          }                    else if( tempToken.equals("*") || tempToken.equals("/") ||                    tempToken.equals("+") || tempToken.equals("-") )          {            if(!postStack.isEmpty())            {              String top = postStack.peek()+"";                             if((top.equals("+") || top.equals("-")) &&                 (tempToken.equals("*") || tempToken.equals("/")))                       precedence = false;                else if (top.equals("("))                  precedence = false;                else                  precedence = true;            }            while( !postStack.isEmpty() &&                     postStack.peek() !="("&& precedence )            {               String top = postStack.peek()+"";                             if((tempToken.equals("+") || tempToken.equals("-")) &&                 (top.equals("*") || top.equals("/")))                       precedence = true;                else if (top.equals("("))                  precedence = true;                else                  precedence = false;                                tokenList.addToFront(postStack.pop());            }                        postStack.push(tempToken);               }                    else   //error handling          {            System.out.println( tempToken + " is illegal");            System.exit(1);          }        }      }    }        while( !postStack.isEmpty() )    {      tokenList.addToFront(postStack.pop());    }        s.close();    int counter = tokenList.size();    ArrayUnorderedList<String> reverseorder =              new ArrayUnorderedList<String>();    for (int i=0; i<counter; i++)      reverseorder.addToRear(tokenList.removeLast());    return reverseorder;  }}