Array Creation and Access
Introduction: 6.1.0
- An
array
is a block or memory which storeselements
of data items of the same type under one name- Useful when you have many elements of the same type to keep track of together
- Each item is stored at an
index
- Like a locker number
- start from index 0
Declaring and Creating an Array: 6.1.1
- To make a variable into an array, put square brackets after the data type
int[] testScores
- An array called
testScores
which is an array of integers
- An array called
- Arrays are
objects
- A variable that declares an array holds a reference to the object
- An uninitialized array is null!
- A variable that declares an array holds a reference to the object
- You can initialize an array using the keyword
new
or aninitalizer list
int[] myArray = new int[6];
int[] yourArray = {3, 4, 5, 6, 7, 8};
int[] theirArray;
theirArray = new int[6];
Using new to Create arrays: 6.1.2
- To create an empty array after declaring a variable, use the
new
keyword with the type and size of the array- This actually creates the array in memory
- Array elements are initialized as normal
- Primitives get their normal default values
- Objects become null
Initializer Lists to Create Arrays: 6.1.3
- Initialize arrays using an
initializer list
- Initialize values of an array to a list of values in curly brackets
- Don’t specify the size
- Primitive type arrays store the values themselves
- Object type arrays store object references
Array Length: 6.1.4
- Arrays know their length
- Available with
arrayName.length
- Available with
Access and Modify Array Values: 6.1.5
- To access array items, use an
indexed array variable
- array name and index inside of square brackets
index
is the position of an item in an array
int[] myArray = {0, 1, 2};
myArray[1] = 17; // myArray == {0, 17, 2};
- to keep track of 5 highest scores in a game with the person who got them, you could use two
parallel arrays
- You need to make sure they stay synchronized!
- If you try to access an element which doesn’t exist, java throws an
ArrayOutOfBoundsException
- You can use variables for array indexes
int index = 7;
myScore = scores[index];
Summary: 6.1.7
- Arrays are collections of related data of all the same data type
- The size of an array is established at the time of creation
- this size is fixed!
- Arrays can store primitive data or object reference types
- When an array is created with
new
all elements are initialized tonull
or default primitive values - Initializer lists can be used to create and initialize arrays
- Square brackets are used to access and modify elements in an array with an index
- Indices range from [0, arr.length - 1]
- Anything outside of that throws an ArrayIndexOutOfBoundsException
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This was adapted from the CS Awesome curriculum, which was created by
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CS Awesome is licensed under CC BY-NC-SA 4.0.