Introduction to Arrays

Chapter 10 Introduction to Arrays

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.

Declaring Arrays • Identify type of array • Use square brackets • int[] myArray; • Declares an array of int values

Instantiating Arrays • Use the new keyword • Identify number of elements • myArray = new int[1000]; • Instantiates myArray with 1000 elements • You can declare and instantiate in one line • int[] myArray = new int[1000];

Putting Values in the Array • Use 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.

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

Determining the Length of the Array • Use 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

Passing by Value • Intrinsic types are passed to methods by value. • A copy of the value is passed. • The original value is unchanged.

Passing by Reference • Objects 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.

Passing Arrays to Methods • An 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

Using Polymorphic Objectsin an Array • An array can hold objects that: • Derive from the same base class • Implement a common interface

Introduction to Arrays