How does a for loop iterate through an array?

Here's a breakdown of how the for-loop is executed (derived from this certification study guide)

Names as referred to below:

for(initialization code; 
    boolean expression; 
    update statements){
  body
}. 

The for-loop's parts are executed in this sequence:

1. Initialization code
2. If boolean expression is true, execute body, else exit the loop
3. Body executes
4. Execute update statements
5. Return to Step 2

So when applied to your example, we can say:

Run initialization:

int i = 0

Iteration 1:

if(i < number.length) // -> if(0 < 3)
//run body
i++ //i becomes 1
//return to step 2 (new iteration)

Iteration 2:

if(i < number.length) // -> if(1 < 3) //i was incremented to 1
//run body
i++ //i becomes 2
//return to step 2 (new iteration)

Iteration 3:

if(i < number.length) // -> if(2 < 3) //i was incremented to 2
//run body
i++ //i becomes 3

Iteration 4 (not run):

//return to step 2 (new iteration)
if(i < number.length) // -> if(3 < 3)  -> condition not met
//condition not met, stop the loop

More specifically, I do not understand how i comes to represent the contents of the array

As you can see above, every time the loop body finishes executing, the update statements are executed, which makes the i variable increment, thus allowing to access a different index of the array.

This is done advisedly, if you change your update statements to i += 2, then some indexes of the array will be skipped.

To access information from an array we must tell the array which part of it we would like to access. To do this we use the syntax

array[index]

When you use a for loop to cycle through an array you are essentially using array[index] to go from the first element to the last.

for (int i = 0; i < array.length; i++) 

Will start at array[0] and got brought to array[lastElement] printing out each element of the array.

The line for(int i = 0; i < number.length; i++) is your clue.

A for-loop, which you are declaring here, specifies three parameters*: An initialization variable, when to continue the loop, and what to do after each iteration:

• int i = 0 is the initialization variable. It's an integer with value 0 that only exists inside the for-loop.
• i < number.length tells the for-loop that it should continue to run any operation inside the for-loop so long as this condition holds. In this case, it means that as long as i is less than the 'length' (or 'size') of your numbers array, it should keep running. That is, as long as i is less than 3.
• i++ tells the for-loop what to do after each iteration. In this case, you're telling the for-loop to increase the variable i by 1.
• System.out.println() is a method that prints stuff to the terminal
• numbers[i] describes that you want whatever element is in the ith index in the numbers array. That is, when i is 2, you want the element in the 2nd index. When i is 1, you want he element in the 1st index. Important note: Java arrays are zero-indexed, which means that the first element in the array has index 0, the second element has index 1, and so on.

What happens in your loop is in other words that you are declaring a loop, that there should be an integer i with the initial value 0, that it should continue to run so long as i is less than 3, that it should increment i by 1 every time it runs, and that every time the loop runs it should print the element at the ith index in the numbers array.

--

*'parameter' is probably not the correct terminology.

Array's values are taken out by the syntax

numbers[index];

Array index is started from 0 then 1 next 2.... So the in order to retrieve the 1st element you need

numbers[0];

Meanwhile inside the for loop you have created a block variable named i. Note that while iterating, the value of the i increases by 1 because of i++.

So in your for loop this happens.

numbers [0];
numbers[1];
numbers[2];

I think what you don't understand is how a for loop works. Please read,

• For loop in Java with example

As per that article,

for(initialization; condition ; increment/decrement){
   statement(s);
}

Example ^{(This is not Java, it's JavaScript but the for loop works the same way; javascript is not java don't misunderstand. I just want to show you a working example on how i's value increments.)} :

var i;
for (i = 0; i < 10; i++) {
  console.log("i = " + i);
}

"Arrays will always be laid out in memory using consecutive storage locations. The compiler knows the array to start at memory cell x. When it needs to get to a[123], it adds 123 to x and uses that number to address the memory to get to the element."

They are in consecutive and indexing starts with 0. and at each new element is next position to the current index. hence you can access any element from an array with his index.

If you are writing numbers[i] means ith element from array. and always highest index of array will always less than length of array (size of array).