[java] How to get a value inside an ArrayList java

Assuming your Car class has a getter method for price, you can simply use

System.out.println (car.get(i).getPrice());

where i is the index of the element.

You can also use

Car c = car.get(i);
System.out.println (c.getPrice());

You also need to return totalprice from your function if you need to store it

main

public static void processCar(ArrayList<Car> cars){
    int totalAmount=0;
    for (int i=0; i<cars.size(); i++){
        int totalprice= cars.get(i).computeCars ();
        totalAmount=+ totalprice; 
    }
}

And change the return type of your function

public int computeCars (){
    int  totalprice= price+tax;
    System.out.println (name + "\t" +totalprice+"\t"+year );
    return  totalprice; 
 }