3 min read•january 8, 2023
Athena_Codes
Athena_Codes
In this unit, we will start learning about data structures, which are structures that store multiple pieces of data. You will learn about three of them in this course: 1-D in this unit, in Unit 7, and in Unit 8. store one type of data, whether that be a or a , and they are of . When used , we can do many things with and build algorithms with them, as well.
In this unit, you will learn three things that are important for larger programs: how to create an array, how to traverse(going through all the elements) an array, and how to manipulate the elements in an array. One of the common mistakes that you may make at first is an , which occurs when you try to access an element where none exists, but with some practice, you will be flawless with !
are used to store one type of data, whether it is a primitive or . themselves are reference types. They are best thought of as a list of items with a , as have a set size that cannot be changed (don’t confuse this with which can also be thought of as a list). are denoted by braces ({}), with items separated by commas such as the following:
{true, true, false, true}
Before we can use , we need to have an import statement, which is
import java.util.
There are two ways to make : using a and using a pre-initialized array.
As with other reference types, we can initialize using a . However, the is slightly different from the constructors from Unit 5:
dataType[] arrayName = new dataType[numberOfItems];
The items in the array are initialized differently depending on the data type. Integers are initialized to 0, doubles are initialized to 0.0, booleans are initialized to false, and all reference types are initialized to null. We will talk about filling constructed lists in the next topic when we discuss .
Pre-initialized
We can also set an array to a pre-initialized array, similar to how we initialize strings. Here, we will initialize an array of 10 integers as follows:
int[] arrayOne = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
We access elements in using bracket notation as follows: arrayName[index]. The most important thing to know is that Java is a , so the first item has index 0, and not 1.
Before we talk about the index of the last item, we need to discuss how to find the array length. The array length is actually an instance variable specific to that particular array denoted as (not to be confused with length() for Strings). Note that this is not a method, so there are no parentheses. Thus, the last item in the array can be accessed by using - 1. Do not confuse this with the in which we use in brackets. If we use an index outside the allowed range, we will get an .
Here is a question: how do we access the even numbers in arrayOne from above?
2 = arrayOne[1]
4 = arrayOne[3]
6 = arrayOne[5]
8 = arrayOne[7]
10 = arrayOne[9]
3 min read•january 8, 2023
Athena_Codes
Athena_Codes
In this unit, we will start learning about data structures, which are structures that store multiple pieces of data. You will learn about three of them in this course: 1-D in this unit, in Unit 7, and in Unit 8. store one type of data, whether that be a or a , and they are of . When used , we can do many things with and build algorithms with them, as well.
In this unit, you will learn three things that are important for larger programs: how to create an array, how to traverse(going through all the elements) an array, and how to manipulate the elements in an array. One of the common mistakes that you may make at first is an , which occurs when you try to access an element where none exists, but with some practice, you will be flawless with !
are used to store one type of data, whether it is a primitive or . themselves are reference types. They are best thought of as a list of items with a , as have a set size that cannot be changed (don’t confuse this with which can also be thought of as a list). are denoted by braces ({}), with items separated by commas such as the following:
{true, true, false, true}
Before we can use , we need to have an import statement, which is
import java.util.
There are two ways to make : using a and using a pre-initialized array.
As with other reference types, we can initialize using a . However, the is slightly different from the constructors from Unit 5:
dataType[] arrayName = new dataType[numberOfItems];
The items in the array are initialized differently depending on the data type. Integers are initialized to 0, doubles are initialized to 0.0, booleans are initialized to false, and all reference types are initialized to null. We will talk about filling constructed lists in the next topic when we discuss .
Pre-initialized
We can also set an array to a pre-initialized array, similar to how we initialize strings. Here, we will initialize an array of 10 integers as follows:
int[] arrayOne = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
We access elements in using bracket notation as follows: arrayName[index]. The most important thing to know is that Java is a , so the first item has index 0, and not 1.
Before we talk about the index of the last item, we need to discuss how to find the array length. The array length is actually an instance variable specific to that particular array denoted as (not to be confused with length() for Strings). Note that this is not a method, so there are no parentheses. Thus, the last item in the array can be accessed by using - 1. Do not confuse this with the in which we use in brackets. If we use an index outside the allowed range, we will get an .
Here is a question: how do we access the even numbers in arrayOne from above?
2 = arrayOne[1]
4 = arrayOne[3]
6 = arrayOne[5]
8 = arrayOne[7]
10 = arrayOne[9]