This document discusses arrays in programming. It begins by defining what an array is - an ordered list that holds multiple elements of the same type. It then covers the basic rules of arrays: they hold only one type of element, cannot change size after creation, start at index 0, and are declared and initialized like variables. The document proceeds to explain how to declare, initialize, access, set and iterate through array elements in code. It provides examples for creating, accessing and modifying arrays, and concludes by assigning further reading on arrays.

1. From last time…
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Please turn in Homework 2!
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We made a beautiful object-oriented night sky!
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Remember that a class has:!
1. a name!
2. attributes (variables)!
3. a constructor (run via ‘new’)!
4. and methods (actions)
!
!
!
!

3. Arrays I
CAP

4. Rules of an Array
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An array is a ordered “list” object which which
holds multiple “elements” (variables or objects)!
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It can hold only “elements” of one type!
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It cannot change size after it has been created!
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It starts at the 0th position!
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An array, like a variable, is declared & initialized

5. Memory
int x;
How does the compiler know!
how much space to reserve?

6. Memory
Type
Bits
Signed?
Min Value
Max Value
byte
8
Yes
-128
127
short
16
Yes
-32768
32767
int
32
Yes
long
64
Yes
etc…
etc…
char (UTF-16)
16
No
0
65535
-2147483648 2147483647

7. Arrays…
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are declared & initialized!
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are ordered!
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hold only elements of one type!
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cannot change size!
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start at 0!
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…why!? Because of memory management.

8. 1. Array Declaration
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Two parts: a type and a name (just like a variable)!
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Brackets after the variable type denote an array
of that variable type:!
! int[] xpositions; // array of integers
float[] widths;
// array of floats
// note that int != int[]

9. 2. Array Initialization
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An array is an object, so we use the new operator!
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Much like variables, we have to give the initial
“state” of the array, which is the size:!
! xpositions = new int[42]; // empty array
widths = new float[78];
// empty array
// size must be an integer! new int[17.2]

10. 1 & 2. One-line Array Creation
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Just like variables we can declare and initialize
arrays in one line:!
int[] xpositions = new int[42];
float[] widths = new float[78];
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Compare to declaring & initializing primitives:!
int xposition = 22;
float width = 32.5;

11. Getting an Element
To access an element in an array: !
arrayName[elementNumber]
int x = xpositions[0];
float myWidth = widths[13];

12. Setting an Element
1. Set single elements:!
! xpositions[0] = 13;
xpositions[1] = 26;
xpositions[2] = 39;
2. “Array Literal,” manually set elements:!
! int[] xpositions = {13,26,39};
// this only works at initialization

13. Demo!
Array Basics &!
Star Coordinates

14. Iteration!
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!
We can iterate through an array using a loop:!
for(int i = 0; i < arrayName.length; i++) {
arrayName[i] = 0; // sets each to 0
}
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!
We can also perform operations in the loop:!
for(int i = 0; i < arrayName.length; i++) {
arrayName[i] += 3; // increments each by 3
}

15. Demo!
Drawing a Line

17. For next time…
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Friday: Quiz 3 (Function, Objects, & Arrays)!
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Monday: Iteration 1 Group Presentations!
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Read Shiffman, p. 153–162 (Arrays II)