Arrays

Read: http://www.learnjavaonline.org/en/Arrays

Read: https://www.javatpoint.com/array-in-java

Two ways to make a new array:

int[] arr = new int[5]; //5 values, at default value, they are 0,0,0,0,0

int[] arr = {1, 2, 3, 4, 5};

You must know the size of the array when you construct it

To set an element to a different value:

arr[0] = 4;

To access the value:

int plusOne = arr[3] +1;

Types of arrays: (for example)

• int[]
• double[]
• String[]
• (the type of every item in the array, plus a pair of brackets)

Every item must match type (for example, you can't have int[] arr={1, 2.5, 3.8, 4}; )

arr.length >to access the length of the array (notice, no parenthesis!)

"Off by one error"

Java arrays are 0 based!

For example: int[] arr = {1,2,3,4,5}; last index is index 4, but the length of the array is 5!

Advanced: there is also two-dimentional arrays (like a spreadsheet)

int arr[][]={{1,2,3},{4,5,6},{7,8,9}};  

if(arr[0][2]==3) //true 

Exercise:

1. Complete the following static method. Return a string for the name of the month.

public static String monthName(int month)

{

//your code

//1. make an array of String. Be careful that arrays are 0 based!

//2. return by accessing the array

}

2. Go to http://codingbat.com/prob/p229948 and do the swapEnds exercise

paste your code after you get a checkmark

Created: Dexin on 3/25/18

Updated: Dexin on 12/9/18