Java Array exercise

Question

I have this array exercise. I want to understand how things work, if someone can

we have the object array of type int called index with 4 elements
we have the object array of type String called islands with 4 elements

I don't understand how things are passing to each other, I need a good explanation.

class Dog {
  public static void main(String [] args) {
    int [] index = new int[4];
    index[0] = 1;
    index[1] = 3;
    index[2] = 0;
    index[3] = 2;
    String [] islands = new String[4];

    islands[0] = "Bermuda";
    islands[1] = "Fiji";
    islands[2] = "Azores";
    islands[3] = "Cozumel";

    int y = 0;
    int ref;

    while (y < 4) {
      ref = index[y];
      System.out.print("island = ");
      System.out.println(islands[ref]);
      y ++;
    }
  }

Consider using a for loop like for (int y = 0; y < 4; y++) instead of your while loop. Just a better style. Anyway what is your question! — SIGKILL
– SIGKILL, Commented Dec 22, 2012 at 11:01
Also note that "homework" tag has been officially deprecated — Pradeep Simha
– Pradeep Simha, Commented Dec 22, 2012 at 11:02
You would need to specify your question a bit better in order to get very good and accurate answer. Otherwise we could write half of a book explaining fundamentals of Java — Tom
– Tom, Commented Dec 22, 2012 at 11:04

grebulon · Accepted Answer · 2012-12-22 11:05:56Z

6

Take a pen and paper and make a table like this, and go through the iterations:

 y    ref    islands[ret]
---   ---    ------------
 0     1      Fiji
 1     3      Cozumel
 2     0      Bermuda
 3     2      Azores

answered Dec 22, 2012 at 11:05

grebulon

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vels4j · Accepted Answer · 2012-12-22 11:05:57Z

0

Well, you've added index in the array named index then accessing the same value in while loop

int y=0;
ref = index[y]; // now ref = 1
islands[ref] // means islands[1] which returns the value `Fiji` that is stored in 1st position

answered Dec 22, 2012 at 11:05

vels4j

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MarioDS · Accepted Answer · 2012-12-22 11:06:50Z

0

First, you make an array that holds ints, the array has length 4 (4 variables can be in it):

int [] intArray = new int[4];

Your array is called index which may be confusing for the explanation. The index of an array is which "position" you are referring to and is between 0 and the length-1 (inclusive). You can use it in two ways:

int myInt = intArray[0]; //get whatever is at index 0 and store it in myInt
intArray[0] = 4; //store the number 4 at index 0

The following code does nothing more than get a number from the first array and use it to access a variable in the second array.

ref = index[y];
System.out.println(islands[ref])

answered Dec 22, 2012 at 11:06

MarioDS

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Mukul Goel · Accepted Answer · 2012-12-22 11:27:40Z

0

To make it understand, take a paper and pen and jot down the arrays in table form and iterate through the loop to understand. (back in school days, our teacher(s) called it a dry run)

First we represent the data

Iteration    y           ref ( `ref = index[y]`)  islands
  1          0                 1                    Fiji 
  2          1                 3                   Cozumel
  3          2                 0                   Bermuda
  4          3                 2                    Azores

So you can go through the iterations Iteration 1

y=0
ref = index[y], i.e. index[0] i.e 1
System.out.print("island = "); prints island = 
System.out.println(islands[ref]); islands[ref] i.e islands[1] i.e Fiji

hence for iteration 1 output will be

island = Fiji

edited Dec 22, 2012 at 11:27

answered Dec 22, 2012 at 11:17

Mukul Goel

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