mirror of
https://github.com/Brandon-Rozek/website.git
synced 2024-12-23 17:51:54 +00:00
160 lines
3.1 KiB
Markdown
160 lines
3.1 KiB
Markdown
# Lecture Notes Oct 2nd
|
|
|
|
## Array
|
|
|
|
`array` is not a reserved word, it's a concept. Arrays are able to hold multiple values under one name of the same type.
|
|
|
|
For instance, you can have an array of integers.
|
|
|
|
Properties of an array
|
|
|
|
- Size (n)
|
|
- index [0, n - 1]
|
|
|
|
You can declare arrays by saying the type '[]' and the name of the array
|
|
|
|
```java
|
|
int[] numbers;
|
|
double[] gpas;
|
|
float[] grades;
|
|
```
|
|
|
|
Before you can use the array, you must `new` it
|
|
|
|
```java
|
|
numbers = new int[10];
|
|
```
|
|
|
|
Where 10 is the size of the array.
|
|
|
|
You can combine both the declaration and initialization
|
|
|
|
```java
|
|
double[] points = new double[7];
|
|
```
|
|
|
|
You can access individual elements of the array by using its index. Indexes start from zero
|
|
|
|
```java
|
|
points[0] = 5.4; // The first element in the point array is 5.4
|
|
```
|
|
|
|
The `.length` property of an array gives the size of the array
|
|
|
|
## For-Loops + Arrays
|
|
|
|
You can print out each element in the array using a for loop
|
|
|
|
```java
|
|
for (int i = 0; i < numbers.length; i++) {
|
|
System.out.println(numbers[i]);
|
|
}
|
|
```
|
|
|
|
You can ask a user to input a value to each element in the array
|
|
|
|
```java
|
|
for (int i = 0; i < points.length; i++) {
|
|
System.out.print("Enter a number: ");
|
|
points[i] = scnr.nextInt();
|
|
}
|
|
```
|
|
|
|
## While-Loops + Arrays
|
|
|
|
You can use a while loop to search the array
|
|
|
|
```java
|
|
int i = 0;
|
|
int number = 5;
|
|
// While the index is within the array size and the number isn't found
|
|
while (i != number.length && number != numbers[i]) {
|
|
i++
|
|
}
|
|
if (i == numbers.length) {
|
|
System.out.println(number + " was not found.")
|
|
} else {
|
|
System.out.println(number + " was found at index " + i)
|
|
}
|
|
```
|
|
|
|
If you don't include the `i != number.length` you will obtain an `IndexOutOfBounds` error.
|
|
|
|
The example above is called a *Linear Search*.
|
|
|
|
Linear searches work on an unsorted and sorted arrays.
|
|
|
|
|
|
|
|
## Methods + Arrays
|
|
|
|
You can pass an array into a method
|
|
|
|
```java
|
|
public static void exampleMethod(int[] sample) {
|
|
// Do something
|
|
}
|
|
public static void main(String[] args) {
|
|
int[] s = new int[30];
|
|
exampleMethod(s);
|
|
}
|
|
```
|
|
|
|
|
|
|
|
## Do-While Loops
|
|
|
|
For-loops can run 0 or more times. If you want something to execute at least once. Use a do-while loop.
|
|
|
|
```java
|
|
do {
|
|
// Code
|
|
} while (condition);
|
|
```
|
|
|
|
For example, to search at least once and asking whether the user wants to search again
|
|
|
|
```java
|
|
// Assume linearSearch and array are defined
|
|
char answer;
|
|
Scanner input = new Scanner(System.in);
|
|
do {
|
|
linearSearch(array, input);
|
|
System.out.print("Do you want to search again? (Y/N) ");
|
|
input.nextLine();
|
|
answer = input.next().charAt(0);
|
|
} while( answer != 'N');
|
|
```
|
|
|
|
You can create any type of loop just by using a while loop.
|
|
|
|
|
|
|
|
## Example: Finding the Max
|
|
|
|
You can find the max of an array using the following method
|
|
|
|
```java
|
|
double max = arrayName[0];
|
|
for (int i = 1; i < arrayName.length; i++) {
|
|
if (max < arrayName[i]) {
|
|
max = arrayName[i];
|
|
}
|
|
}
|
|
System.out.println("The max is " + max);
|
|
```
|
|
|
|
|
|
|
|
## Example: Summing up an array
|
|
|
|
You can sum the array using the following method
|
|
|
|
```java
|
|
double sum = 0;
|
|
for (int i = 0; i < arrayName.length; i++) {
|
|
sum += arrayName[i];
|
|
}
|
|
System.out.println("The sum is " + sum);
|
|
```
|
|
|