1. Chapter 6 Arrays
Fall CS2302: Programming Principles

2. Store a large number of values during the execution of a program.
Why array?
Store a large number of values during the execution of a program.
What is array?
A fixed-size sequential collection of elements of the same type.
The Open Systems Interconnection (OSI) model is a product of the Open Systems Interconnection effort at the International Organization for Standardization (ISO).
Fall CS2302: Programming Principles

3. Declaration: Example: Basic Operations elementType[ ] arrayRefVar;
double[ ] myList;
Fall CS2302: Programming Principles

4. Declaring and Creating in one step:
Basic Operations
Creation:
arrayRefVar = new elementType[arraySize];
Example:
myList = new double[10];
Declaring and Creating in one step:
dobule[ ] myList = new double[10];
Fall CS2302: Programming Principles

5. Element identification:
Basic Operations
Element identification:
arrayRefVar[index];
Example:
myList[9]; // represents the last element in the array myList.
Index range:
From 0 to arrayRefVar.length - 1
Fall CS2302: Programming Principles

6. Assigning values Example: Basic Operations arrayRefVar[index] = value;
myList[5] = 34.33;
Fall CS2302: Programming Principles

7. Array initialization with declaration
Basic Operations
Array initialization with declaration
Declaring, creating, initializing in one step:
double[ ] myList = {1.9, 2.9, 3.4, 3.5};
Fall CS2302: Programming Principles

8. Objectives Pass arrays to methods Return an Array from a method
Reverse Arrays
Partially Filled Arrays
Insert into a partially filled array
Fall CS2302: Programming Principles

9. Pass by value
Most methods are passed arguments when they are called. An argument may be a constant or a variable.
Math.sqrt(33)
Math.sqrt(x)
If a variable is passed, the method receives a copy of the variable's value. The value of the original variable cannot be changed within the method.
because the method only has a copy of the value; it does not have access to the original variable.
This process is called pass by value.
Fall CS2302: Programming Principles

10. Pass by Value
public class TestPassByValue { /** Main method */ public static void main(String[] args) { // Declare and initialize variables int num1 = 1; int num2 = 2; System.out.println("Before invoking the swap method, num1 is " num1 + " and num2 is " + num2); // Invoke the swap method to attempt to swap two variables swap(num1, num2); System.out.println("After invoking the swap method, num1 is " num1 + " and num2 is " + num2); } /** swap method - Swap two variables */ public static void swap(int n1, int n2) { System.out.println("\tInside the swap method");
System.out.println("\t\tBefore swapping n1 is " + n " n2 is " + n2); // Swap n1 with n2 int temp = n1; n1 = n2 n2 = temp; System.out.println("\t\tAfter swapping n1 is " + n " n2 is " + n2); } }
Fall CS2302: Programming Principles

11. Passing Arrays to Methods
public static void printArray(int[] array) {
for (int i = 0; i < array.length; i++) {
System.out.print(array[i] + " "); }
//Invoke the method
int[] list = {3, 1, 2, 6, 4, 2}; //initialize array
printArray(list);
//Invoke the method
printArray(new int[]{3, 1, 2, 6, 4, 2});
Anonymous array
Fall CS2302: Programming Principles

12. Simple Example public class Test {
public static void main(String[] args) {
int x = 1; // x represents an int value
int[] y = new int[10]; // y represents an array of int values
m(x, y); // Invoke m with arguments x and y
System.out.println("x is " + x);
System.out.println("y[0] is " + y[0]); }
public static void m(int number, int[] numbers) {
number = 1001; // Assign a new value to number
numbers[0] = 5555; // Assign a new value to numbers[0]
Fall CS2302: Programming Principles

13. Passing Arrays as Arguments
Objective: Demonstrate differences of passing primitive data type variables and array variables.
TestPassArray
Run
Fall CS2302: Programming Principles

14. Objectives Pass arrays to methods Return an Array from a method
Reverse Arrays
Partially Filled Arrays
Insert into a partially filled array
Fall CS2302: Programming Principles

15. Objectives Pass arrays to methods Return an Array from a method
Reverse Arrays
Partially Filled Arrays
Insert into a partially filled array
Fall CS2302: Programming Principles

16. Ending a Loop with a Sentinel Value
Often the number of times a loop is executed is not predetermined. You may use an input value to signify the end of the loop. Such a special input values is known as a sentinel value.
Write a program that reads and calculates the sum of an unspecified number of integers. The input 0 signifies the end of the input.
SentinelValue
Run
Fall CS2302: Programming Principles