Using array names correctly in for each loop

Question

Given the following example code, please help me answer the following questions with hints

 public class Coin
    {
    private String myColor;
    private int mySideOne;
    private double mySideTwo;


    public Coin(String Color, int SideOne, double SideTwo)
    {
    myColor= Color;
    mySideOne = SideOne;
    mySideTwo = SideTwo;
    }
    //accessors getColor(), getSideOne(), and getSideTwo()

}

public class Total
{
private int myNumCoins;
private Coin[] moneyList;

//constructor
public Total(int myCoins)

{

myNumCoins = numCoins;
moneyList = new Coins[numCoins]
String color;
int mySideOne;
double mySideTwo;
for (int i = 0; i<numCoins; i++)
{




}
}

**

Question:

**

//Returns total amount for Coins 
public double totalMoney()
{
double total = 0.0;
/* code to calculate 
return total;
}
}

Which represents correct / code to calculate amount */ in the totalMoney method?

 A. for (Coin t: moneyList)
    total+= moneyList.getSideTwo();

    B. for (Coin t: moneyList)
    total+=t.getSideTwo();

I think A is right because the "t" in B. doesn't exist in the code. How am I wrong?

A won't even compile, there isn't a getPrice() method on an array. — JimW
– JimW, Commented Jan 13, 2015 at 21:47
I might be wrong, but you dont have tickList and if you do make sure it is static — Asif Alamgir
– Asif Alamgir, Commented Jan 13, 2015 at 21:48
@JimW is right. Option A won't compile. Option B is the enhanced for loop where t is a local variable just the way i is in the regular for loop — SDS
– SDS, Commented Jan 13, 2015 at 21:50
@AmandaKelius tickList is a collection of Ticket objects. The collection has it's own properties like "how many objects do I have" and each item in the collection has it's own set of properties like "price" For a real world example think of a parking lot full of cars. The lot could be full, you could start one of the cars but you can't "start" the parking lot. — JimW
– JimW, Commented Jan 13, 2015 at 22:08

Luiggi Mendoza · Accepted Answer · 2015-01-13 22:37:57Z

3

Let's evaluate the code using A.:

public double totalPaid()
{
    double total = 0.0;
    for (Ticket t:tickList)
        total+= tickList.getPrice();
    return total;
}

tickList is an array of Tickets. An array is an object which only has a static final field called length. So, tickList cannot have getPrice. This means, option A doesn't compile.

Let's evaluate the code using B.:

public double totalPaid()
{
    double total = 0.0;
    for (Ticket t:tickList)
        total+=t.getPrice();
    return total;
}

Here you state:

I think A is right because the "t" in B. doesn't exist in the code. How am I wrong?

In fact, t is a variable declared and used in the enhanced for loop statement. t is from type Ticket and it will take the value of each Ticket object reference stored in tickList. The enhanced for loop can be translated to this form for arrays:

for (int i = 0; i < tickList.length; i++) {
    Ticket t = tickList[i];
    //use t in this scope
    //in this case, it's used to accumulate the value of total
    total += t.getPrice();
}

Which makes B as the solution for this problem.

edited Jan 13, 2015 at 22:37

answered Jan 13, 2015 at 21:49

Luiggi Mendoza

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2 Comments

Luiggi Mendoza Over a year ago

@AmandaKelius tickList is not part of the constructor. tickList is a field declared in Transaction class. Check here: private Ticket[] tickList;. This field is initialized in the constructor of Transaction class: tickList = new Ticket[numTicks]. You cannot directly access to the methods of the elements of the array using the array variable only, you have to access to a single element in the array and then access to its elements, as shown in the code above.

Luiggi Mendoza Over a year ago

@AmandaKelius no, t is a Ticket t, it's a single Ticket. You can see the difference in the last piece of code in my answer.

haley · Accepted Answer · 2015-01-13 21:48:52Z

2

The answer is B because you declare t in your loop when you say Ticket t. The loop iterates the ticketList and t will stand for each Ticket in the list.

answered Jan 13, 2015 at 21:48

haley

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