1. 1D Arrays and Lots of BracketsPs
Module 7 – Part I
1D Arrays and Lots of Brackets
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CSE 1321 Module 7

2. 2. Creating and Initializing Arrays
You must choose: 1) Create an empty arrays and assign initial values with a loop later on: CREATE myArray[5] OR 2) Create and initialize the array in one line. This is helpful when we already know those value (e.g. days of the week, etc.).
4/6/2019
CSE 1321

3. Array Creation Example
1) Create an empty array. By default, 0s are stored in the array.
int[] myArray = new int[5];
2) Creates and initializes in one line. The stored values are show in { }; int[] myArray = {10, 20, 30, 40, 50};
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CSE 1321

4. 3. Accessing Information
Copy information out of a particular slot
Example:
CREATE clientAge // Integer
clientAge ← myArray[4]
This copies information from the fifth slot (slot four) into the variable clientAge
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CSE 1321

5. Horrible, but works…
// creates empty array with 5 slots, 0-4 CREATE myArray [5] //Assigns literal values to each index in the array. myArray[0] ← 10 myArray[1] ← 20 myArray[2] ← 30 myArray[3] ← 40 myArray[4] ← 50 Ps
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CSE 1321

6. Accessing and Modifying
//Accessing int secondNumber = myArray[1]; PRINT(secondNumber);
//Modifying myArray[3] = 42; PRINT(myArray[3]);
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CSE 1321 Module 4

7. Ps Traversing the Array
You will use a loop to visit every cell of the array
Problem: create an array of 5 bytes and fill each slot with the number 42
Solution:
CREATE myArray [5]
FOR i ← 0 to 4
myArray[i] ← 42
END FOR Ps
4/6/2019
CSE 1321

8. Traversing an Array
Use a FOR, WHILE or DO-WHILE starting at index 0 and going thru .length-1
for (int i=0; i < data_storage.length; i++)
{ // do something }
OR use a foreach loop
foreach (int t : data_storage)
{ //do something as long as it is not assignment }
4/6/2019
CSE 1321

9. Ps Another Trace CREATE smallestSoFar smallestSoFar ← randomArray[0]
FOR counter ← 1 to 4
IF (smallestSoFar > randomArray[counter]) THEN
smallestSoFar ← randomArray[counter]
END IF
END FOR
// Done
counter 5 1 2 3 4
smallestSoFar -8 42 17 42 -8 4

10. Finding the Minimum using a Method
private static int FindMin (int[] A) {
int temp = A[0];
for (int i = 1; i < A.length(); i++) {
if (temp > A[i])
{ temp = A[i];} }
return temp;
Parameters match in position and type, so the name doesn't matter. Arrays are a reference type in Java.
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CSE 1321

11. Finding the sum or average using a method
METHOD FINDAVERAGE ( parameter: nums[]) BEGIN sum ← 0 FOR i ← 0 to nums.length - 1 // MOST IMPORTANT LINE IS HERE sum = sum + nums[i] ENDFOR average = sum / nums.length return average END FINDAVERAGE Ps
4/6/2019
CSE 1321

12. Finding a sum and or average using a method
private static float FindAverage (int [] B) {
int sum = 0;
for (int i = 0; i < B.length; i++)
sum += B[i]; }
return (float)sum / B.length;
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CSE 1321

13. Ps Defining a 2D array CREATE array nums [numRows][numColumns]
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CSE 1321

14. Java- Define a 2D Array
<type> [ ][ ] <name> = new <type>[<rowSize>][<columnSize>];
For example:
int[ ][ ] grid = new int [10][20];
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CSE 1321

15. Working with 2D arrays
Usually involves nested loops, as shown below Problem Statement: Create an array of 4 rows and 5 columns. Populate the array with the numbers 1-20.
Create array grid[4][5] count ← 1
FOR each element in a row
FOR each element in a column     grid[row][col] = count
count ← count + 1
END INNER FOR END FOR
4/6/2019
CSE 1321

16. Working with 2D arrays class Main {
public static void main(String[] args) {
int count = 1;
//declare a 2D array with 4 rows and 5 columns
int[][] grid = new int[4][5];
//getting the rows in the array
for (int row = 0; row < 4; row++) {
//populate the values in the array (row) we're currently on from the outer loop
for (int column = 0; column < 5; column++){
grid[row][column] = count;
count++; }
//for each array in the grid (represented by rows)
for(int item[] : grid)
//for each element in the array (row) we're currently on from the outer loop
for (int number : item) {
System.out.print(number + ",");
if(number % 5 == 0)
{ System.out.println(" "); }
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CSE 1321

17. Working with Array Lists
import java.util.ArrayList;
class Main {
public static void main(String[] args) {
//declare variables
int n = 2;
//create list
ArrayList<String> colors = new ArrayList<String>(n);
//add colors
colors.add("purple");
colors.add("pink");
colors.add("green");
System.out.println("Does the arraylist contain the color pink?");
if (colors.contains("pink")) {
System.out.println("Yes");
System.out.println("\n");
} else {
System.out.println("No"); }
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CSE 1321

18. Working with Array Lists
CONTINUED FROM PREVIOUS SLIDE
//indexOf returns the position of the argument
System.out.println("Which position is pink in?");
System.out.println(colors.indexOf("pink"));
System.out.println("\n");
//remove removes the argument from the list
colors.remove("purple");
//get() references the position in the arraylist
System.out.println("The item in index 1 of the list is:");
System.out.println(colors.get(1));
//items are stored as objects and can be referenced as such
System.out.println("The Colors Arraylist:");
for(Object o : colors) {
System.out.println(o); }
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CSE 1321