Instead of
obj1=(int) calStack.topAndpop();//check how this casting is done
obj2=(int)calStack.topAndpop();
Use:
obj1 = Integer.parseInt((String)calStack.topAndpop());
obj2 = Integer.parseInt((String)calStack.topAndpop());
Question
I am trying to write a code for postfix evaluation but I get a error as
java.lang.String cannot be cast to java.lang.Integer and the problem is in the linesobj1=(int) calStack.topAndpop();
.The problem is my ArrayStack topAndpop() method returns a Object type as
public Object topAndpop() throws EmptyStackException{
Object returnPop;
if (isEmpty())
throw new EmptyStackException("Stack empty");
else{
returnPop=top();
pop();
}
return returnPop;
and I should be able to convert this into int type.I can't see anything wrong apart from this line.Can someone point me how to correct this please
import java.lang.Math;
public class Calculate{
double result=0;
int obj1,obj2;
public Object cal(String expression) throws OverFlowException,EmptyStackException{
String[] array = expression.split("");//remember
// for (int i=0;i<array.length;i++)
// System.out.println(array[i]);
ArrayStack calStack=new ArrayStack(array.length);
for(int i=0;i<array.length;i++){
if(!(array[i].equals("+") || array[i].equals("-")||array[i].equals("/") || array[i].equals("*"))){
calStack.push(array[i]);
//calStack.print();
}
else {
obj1=(int) calStack.topAndpop();//check how this casting is done
obj2=(int)calStack.topAndpop();
result=calculate(obj2,obj1,array[i]);
System.out.println(result);
calStack.push(result);
}
}
return calStack.topAndpop();
}
public double calculate(int a,int b,String op){
if(op=="+")
return a+b;
else if(op=="-")
return a-b;
else if(op=="/")
return a/b;
else if (op=="^")
return Math.pow(a,b);
else
return a*b;
}
public static void main (String args[]) throws OverFlowException,EmptyStackException{
Calculate c=new Calculate();
System.out.println("result"+c.cal("623+-382/+*2^3"));
}
}
La solution
Instead of
obj1=(int) calStack.topAndpop();//check how this casting is done
obj2=(int)calStack.topAndpop();
Use:
obj1 = Integer.parseInt((String)calStack.topAndpop());
obj2 = Integer.parseInt((String)calStack.topAndpop());
Autres conseils
You have more then one issue, first String equality -
public double calculate(int a,int b,String op){
if(op.equals("+")) // <-- .equals! Not ==
return a+b;
else if(op.equals("-"))
return a-b;
else if(op.equals("/"))
return a/b;
else if(op.equals("^"))
return Math.pow(a,b);
else
return a*b;
}
Next, since your Stack doesn't appear to be generic, you should call Integer.parseInt(String),
obj1 = Integer.parseInt(calStack.topAndpop().toString());
The problem is in the if condition where you check for symbols, In this you have missed the ^
symbol :
if(!(array[i].equals("+") || array[i].equals("-")
||array[i].equals("/") || array[i].equals("*"))){
Add the condition for ^
symbol as follows and your code will work :
if(!(array[i].equals("+")
|| array[i].equals("-")
||array[i].equals("/")
|| array[i].equals("*"))
|| array[i].equals("^"))){
// do something
}