u can try the follwing coding
import java.io.*;
import java.util.*;
//begin coding for the stack interface
interface Stack<E>
{
public boolean isEmpty();//tests is current stack is empty. Returns true if so, and false if not.
public E top() throws StackException;//retrieves value at the top of the stack. Stack cannot be empty.
public void push(E value) throws StackException;//pushes a value on the top of the stack.
public void pop() throws StackException;//removes a value from the top of the stack. Stack cannot be empty.
}//terminates coding of Stack interface
//begin coding for the objArrayStack class
class objArrayStack<E> implements Stack<E>
{
//constructor
public objArrayStack()
{
topValue=-1;
}//terminates constructor
public void push(E value)throws StackException
{
if(topValue<ArraySize-1)//currrent stack is not full
{
++topValue;
Info[topValue]=value;
}//terminates if
else //current stack is full
throw new StackException("Error: Overflow");
}//terminates push method
public void pop() throws StackException
{
if(!isEmpty())//current stack is not empty
--topValue;
else //stack is empty
throw new StackException("Error: Underflow");
}//terminates pop method
public boolean isEmpty()
{
return topValue==-1;
}//terminates isEmpty method
public E top() throws StackException
{
if(!isEmpty())//stack is not empty
return (E)Info[topValue];
else //stack is empty
throw new StackException("Error: Underflow");
}//terminates top method
//declare instance variables
final int ArraySize=10;
private Object Info[]=new Object[ArraySize];
private int topValue;
//begins coding for the StackException class
class StackException extends RuntimeException
{
//constructor
public StackException(String str)
{
super(str);
}//terminates text of constructor
}//terminates text of StackException class
//method to convert from infix to postfix notation
public static String InToPost(String infixString)
{
//operator stack initialized
objArrayStack<Character> operatorStack = new objArrayStack<Character>();
//postfix string initialized as empty
String postfixString = " ";
//scan infix string and take appropriate action
for(int index = 0; index < infixString.length(); ++index)
{
char chValue = infixString.charAt(index);
if(chValue == '(')
operatorStack.push('(');
else if(chValue == ')')
{
Character oper = operatorStack.top();
while(!(oper.equals('(')) && !(operatorStack.isEmpty()))
{
postfixString += oper.charValue();
operatorStack.pop();
oper = operatorStack.top();
}//end while loop
operatorStack.pop();
}//end else if
else if(chValue == '+' || chValue == '-')
{
if(operatorStack.isEmpty()) //operatorStack is empty
operatorStack.push(chValue);
else //current operatorStack is not empty
{
Character oper = operatorStack.top();
while(!(operatorStack.isEmpty() || oper.equals(new Character('(')) || oper.equals(new Character(')'))))
{
operatorStack.pop();
postfixString += oper.charValue();
}//ends while loop
operatorStack.push(chValue);
}//end else
}//end else if
else if(chValue == '*' || chValue == '/')
{
if(operatorStack.isEmpty())
operatorStack.push(chValue);
else
{
Character oper = operatorStack.top();
while(!oper.equals(new Character('+')) && !oper.equals(new Character('-')) && !operatorStack.isEmpty())
{
operatorStack.pop();
postfixString += oper.charValue();
}//end while loop
operatorStack.push(chValue);
}//end else
}//end else if
else
postfixString += chValue;
}//end for loop
while(!operatorStack.isEmpty())
{
Character oper = operatorStack.top();
if(!oper.equals(new Character('(')))
{
operatorStack.pop();
postfixString += oper.charValue();
}//end if
}//end while
return postfixString ;
}//terminates text of InToPost method
public static void main(String[]args)
{
objArrayStack mystack = new objArrayStack();
System.out.println("Enter a string");
Scanner scan = new Scanner(System.in);
scan.nextLine();
String str = scan.nextLine();
InToPost(str);
}//terminates text of main method
}//terminates text of objArrayStack class
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