Funktionsplotter - Programmierung

public void Berechnung(String expr){
	String cleanExpr = cleanExpr(expr);
		LinkedList<Double> stack = new LinkedList<Double>();
		for(String token:cleanExpr.split("\\s")){
			Double tokenNum = null;
			try{
				tokenNum = Double.parseDouble(token);
			}catch(NumberFormatException e){}
			if(tokenNum != null){
				stack.push(Double.parseDouble(token+""));
				}else if(token.equals("*")){
				double secondOperand = stack.pop();
				double firstOperand = stack.pop();
				stack.push(firstOperand * secondOperand);
			}else if(token.equals("/")){
				double secondOperand = stack.pop();
				double firstOperand = stack.pop();
				stack.push(firstOperand / secondOperand);
			}else if(token.equals("-")){
				double secondOperand = stack.pop();
				double firstOperand = stack.pop();
				stack.push(firstOperand - secondOperand);
			}else if(token.equals("+")){
				double secondOperand = stack.pop();
				double firstOperand = stack.pop();
				stack.push(firstOperand + secondOperand);
			}else if(token.equals("^")){
				double secondOperand = stack.pop();
				double firstOperand = stack.pop();
				stack.push(Math.pow(firstOperand, secondOperand));
			}
		}
		y1.setText("Y1:"+stack.pop());
	}

import java.util.*;  
public class ShuntingYard {   
  
private enum Operator   {         
ADD(1), SUBTRACT(2), MULTIPLY(3), DIVIDE(4);         
final int precedence;         
Operator(int p) { precedence = p; }     
}      
private Map<String, Operator> ops = new HashMap<String, Operator>() {{         
put("+", Operator.ADD);         
put("-", Operator.SUBTRACT);         
put("*", Operator.MULTIPLY);         
put("/", Operator.DIVIDE);     }}; 
    
 private boolean isHigerPrec(String op, String sub)     {         
return (ops.containsKey(sub) && ops.get(sub).precedence >= ops.get(op).precedence);     }      

public TextView RPN(View view)     {

String Function = getIntent().getStringExtra("funktion");
StringBuilder output = new StringBuilder();         
Deque<String> stack  = new LinkedList<>();          

for (String token : Function.split("\\s")) {            
 // operator            
if (ops.containsKey(token)) {                 
while ( ! stack.isEmpty() && isHigerPrec(token, stack.peek()))                    
output.append(stack.pop()).append(' ');                 
stack.push(token);             
 // left parenthesis             
}else if (token.equals("(")) {                 
stack.push(token);             
 // right parenthesis             
} else if (token.equals(")")) {                
 while ( ! stack.peek().equals("("))                     
output.append(stack.pop()).append(' ');                 
stack.pop();              
// digit            
 } else {                 
output.append(token).append(' ');            
 }         
}         
 while ( ! stack.isEmpty())             
output.append(stack.pop()).append(' ');         
 output.toString()
Output.setText(output)
return Output
 }  
}