Array Instantiation

Question

Can you help me out with this question please.

Question: Given the following array declarations

double readings[];
String urls[];
TicketMachine[] machines;

write assignments that accomplish the following tasks:

• make the readings variable refer to an array that is able to hold sixty double values
• make the urls variable refer to an array that is able to hold ninety String objects
• make the machines variable refer to an array that is able to hold five TicketMachine objects

My answer:

//declare and instantiate object

double readings [] = new double [60];

String urls [] = new String [90];

TicketMachine machines [] = new TicketMachine [5];

The error I am getting is this:

Main.java:16: readings is already defined in main(java.lang.String[])

double readings [] = new double [60];
       ^

Main.java:17: urls is already defined in main(java.lang.String[])

String urls [] = new String [90];
       ^

Main.java:18: machines is already defined in main(java.lang.String[])

TicketMachine machines [] = new TicketMachine [5];

Answer 1

Once you declare the variables, you don't need to mention their type again on future assignments.

Thus, if you do:

int i;
int i = 5;

then you've redeclared the type of i, which is an error. Instead, just do:

int i;
i = 5;

Or even better, you can combine the two into one statement:

int i = 5;

Since the variables in your particular example have already been declared as a particular type, then you can just do:

readings = ...;
urls = ...;
machines = ...;

Answer 2

Use the clues that the compiler is giving you to track down the root cause of the problem. This is an important skill in becoming a competent programmer.

Answer 3

you've already declared those variables, so now you can just instantiate them

readings = new double[60];
urls = new String[90];
machines = new TicketMachine[5];