Postfix & Infix

public class Node {
char data;
Node next;
public Node(){
}
public Node(char info,Node n){
this.data=info;
this.next=n;
}
public char getData(){
return this.data;
}
public void setData(char data){
this.data=data;
}

public Node getNext(){
return this.next;
}

public void setNext(Node next){
this.next = next;
}
}
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private static Node topNode;
private static int size;

public static boolean isEmpty(){
return (topNode==null);
}
public static int size(){
return size;
}

public static void push(char ch){
Node newNode = new Node(ch,null);
if(isEmpty())
topNode = newNode;
else{
newNode.setNext(topNode);
topNode = newNode;
}
}

public char pop(){
char temp=' ';
if(!isEmpty()){
temp = topNode.getData();
topNode = topNode.getNext();
}
return temp;
}
public char top(){
if(isEmpty())
System.out.println("Empty stack");
return topNode.getData();

}


}

public class Stack{

private Stack myStack;
String output="";
String input;
public convert(String input) {
this.input = input;
myStack = new Stack();
}
public void getOperand(char op, int prec1){
while(!myStack.isEmpty()){
char topop = myStack.pop();
if(topop=='('){
myStack.push(topop);
break;
}
else {
int prec2;
if (topop == '+' || topop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1)
{
myStack.push(topop);
break;
} else

output = output + topop;
}
}
myStack.push(op);
}
public void parenth(char ch){
while (!myStack.isEmpty()) {
char x = myStack.pop();
if (x == '(')
break;
else
output = output + x;
}
}
public String prec() {
int num1, num2, ans;
num2 = myStack.pop();
num1 = myStack.pop();
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case '+':
case '-':
getOperand(ch,1);
break;
case '*':
case '/':
getOperand(ch, 2);
break;
case '^':
getOperand(ch,3);
break;
case '(':
myStack.push(ch);
break;
case ')':
parenth(ch);
break;
default: // Operand
output = output + ch;
break;
}
}
while (!myStack.isEmpty()) {
output = output + myStack.pop();

}
System.out.println(output);
return output;//postfix
}

//Evaluation
public void evaluate() {
char a;
char b;
for (int j = 0; j < output.length(); j++) {
int result = 0;
char ch = output.charAt(j);
switch (ch) {
case '+':
a = myStack.pop();
b = myStack.pop();
result = a + b;
myStack.push(result);
break;
case '-':
a = myStack.pop();
b = myStack.pop();
result = a - b;
myStack.push(result);
break;
case '*':
a = myStack.pop();
b = myStack.pop();
result = a * b;
myStack.push(result);
break;
case '/':
a = myStack.pop();
b = myStack.pop();
result = a / b;
myStack.push(result);
break;
default:
myStack.push(ch);
break;
}
}
System.out.println(myStack.pop());
}
}

public class convert{