Chapter 8 Arrays and the arraylist class 2

Chapter 8 Chapter 8 Arrays and the ArrayList Class Arrays of Objects 2 Contents I String Arrays II Arrays of Objects III Command Line Arguments and Variable Length Argument Lists 3 I String Arrays 1 C.

Chapter 8

Arrays and the

ArrayList Class

Arrays of Objects

I String Arrays

II Arrays of Objects

III Command-Line Arguments and

Variable-Length Argument Lists

I String Arrays

1 Creating String Arrays

2 Calling String Methods from an Array

Element

I.1 Creating String Arrays

In memory, an array of String objects is

arranged differently than an array of a primitive

data type

An array of String objects is really an array of references to String objects

Creating an array of String objects initialized

with values:

String[] names = {“Bill”, “Susan”, “Steven” };

I.1 Creating String Arrays

address address

“Bill” “Susan” “Steven”

The names variable holds the

address of a String array

The String array is

an array of references

to String objects

I.1 Creating String Arrays

Creating an initialized array of String objects:

String[] names = new String[3];

null null

The names variable holds the address of a String array

The String array is

an array of references

to String objects

I.1 Creating String Arrays

When we create an initialized array of String

objects, we must assign a value to each element

in the array that we intend to use

String[] names = new String[3];

names[0] = “Bill”;

names[1] = “Susan”;

names[2] = “Steven”;

I.2 Calling String Methods from

an Array Element

Each element of a String array is a String

object, we can use an element to call a String

method

 //Declare a char variable named letter

char letter;

//Assign the first character in names[3] to letter.

An element of the names array

I.2 Calling String Methods from

an Array Element

The following loop displays the length of each

string held in names:

for(int i = 0; i < names.length; i++)

System.out.println(names[i].length());

8.15

a Write a statement that declares a String array initialized with the following strings: “Mercury”,

“Venus”, “Earth”, and “Mars”

b Write a loop that displays the contents of each element in the array you declared in a

c Write a loop that displays the first character of the strings stored in each element of the array you declared in a

II Arrays of Objects

Like any other data type, we can create arrays of class objects

BankAccount[] accounts = new BankAccount[5];

The variable that references the array is named accounts

As with String arrays, each element in this

array is a reference variable

II Arrays of Objects

We must individually create the objects that each element will reference

for(int index = 0; index < accounts.length; index++)

accounts[index] = new BankAccount();

8.16 Write a Rectangle class Write code that declares a Rectangle array with five elements Instantiate each element with a Rectangle

object Use constructor to initialize each object

with values for the length and width fields

III Command-Line Arguments and Variable-Length Argument Lists

1 Command-Line Arguments

2 Variable-Length Argument Lists

III.1 Command-Line Arguments

Consider the main method's header:

public static void main(String[] args)

The parameter args is an reference to an arry of String

The array that is passed into the args parameter comes from the operating system command-line

III.1 Command-Line Arguments

/**

This program displays the arguments passed to it from the operating system command line.

*/

public class CommandLine

{

public static void main(String[] args)

{

for(int index; index < args.length; index++)

System.out.println(args[index]);

}

}

 Compile and the execute with the following command:

java CommandLine Good morning

III.2 Variable-Length Argument

Lists

Java provides a mechanism known as

variable-length argument lists.

We can write a method that takes a variable

number of arguments

The method that accepts any number of

arguments when it is called

The parameter is known as a vararg parameter.

int sum( int numbers )