Introduction to Arrays

Chapter 10

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What is an array?An array is an ordered collection that stores many elements of the same type within one variable name.

Elements are the items in an array.

Each element is identified with an index number.

Index numbers always start at 0 for the first element.

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Declaring ArraysIdentify type of array

Use square bracketsint[] myArray;

Declares an array of int values

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Instantiating ArraysUse the new keyword

Identify number of elementsmyArray = new int[1000];

Instantiates myArray with 1000 elements

You can declare and instantiate in one line

int[] myArray = new int[1000];

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Putting Values in the ArrayUse the index operator to assign a value at a particular place in the array.myArray[10] = 100;

Assigns the value 100 to the 10th element in the array

Most programs use a for loop to iterate the array.

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Initializing the ArrayYou can initialize the array with values at the same time the array is created.int[] myArray = {1, 2, 3, 4, 5};

10Determining the Length of the

ArrayUse the length property to find the number of elements in the array.System.out.println(myArray.length);

Displays the length of the array in the console

For ( int i = 0; i < myArray.length; i++ );

Uses the length property to set up the for loop

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Passing by ValueIntrinsic types are passed to methods by value.

A copy of the value is passed.

The original value is unchanged.

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Passing by ReferenceObjects are passed to methods by reference.

The reference points to the original object.

A change to the object affects the object in the calling method.

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Passing Arrays to MethodsAn array is an object type.

Passed by reference

Elements of arrays are not necessarily passed by reference.

Depends on the underlying element type

Extracting int elements from an array and passing them to a method passes them by value

10Using Polymorphic Objects

in an ArrayAn array can hold objects that:

Derive from the same base class

Implement a common interface