Java Arrays [Lists] in 10
Minutes
Declaring an array (and its types)
int[] myIntArray;
double[] myDoubleArray;
String[] myStrings;
//What’s the pattern?
//dataType[] arrayName;
//Note: the arrays don’t really exist yet!
Initializing an array
int[] myIntArray = new int[4];
double[] myDoubleArray = new double[5];
String[] myStrings = new String[3];
//What’s the pattern?
//dataType[] arrayName = new
dataType[size];
//Now we’ve allocated new space for the
arrays
//Each array element has a default 0 value
Explicit initialization
//or we can explicitly initialize the arrays
int[] myIntArray = { 4, 2, 6, 8 };
double[] myDoubleArray = { 1.0, 2.3, 6.3, 7.5, 0.1 };
String[] myStrings = {“lol”,“omg”,“ROTFLSHMSFOAIDMT”}
//Note: use { } and separate elements with commas
Size/length of an array
int[] myIntArray = { 4, 2, 6, 8 };
System.out.println( myIntArray.length );
//prints 4
//Note: length has no () with arrays!!!!
Accessing an array element
int[] myIntArray = { 4, 2, 6, 8 };
System.out.print( myIntArray[0] ); //prints 4
System.out.print( myIntArray[2] ); //prints 6
System.out.print( myIntArray[myIntArray.length-1] );
//prints 8
//Each element in the array has an index
//Indices start at 0 and end at length-1
Changing/setting an array element
int[] myIntArray = { 4, 2, 6, 8 };
myIntArray[0] = 9;
//myIntArray now has [9, 2, 6, 8]
myIntArray[1] = myIntArray[2];
//myIntArray now has [9, 6, 6, 8]
Loops and arrays
//Example of linear traversal of array
int[] myIntArray = { 4, 2, 6, 8 };
for (int i = 0; i < myIntArray.length; i++)
{
System.out.println(myIntArray[i]);
}
//Try out on your own the same loop and print
out all the words in:
String[] myStrings =
{“lol”,“omg”,“ROTFLSHMSFOAIDMT”}
Initialize array elements with a loop
//Traverse the array and set each element to 3
int[] myIntArray = { 4, 2, 6, 8 };
for (int i = 0; i < myIntArray.length; i++)
{
myIntArray[i] = 3;
}
Reference variables
 Array variables are actually references to
the arrays
Example:
int[] myIntArray = new int[4];
int[] array2 = myIntArray;
//How many arrays are there? (Hint: How
many times did we say “new”?
//How many array references are there? (Hint:
How many times did we say “int[]”?
Reference Variables cont’d
int[] myIntArray = { 4, 2, 6, 8 };
int[] array2 = myIntArray;
array2[0] = 0;
System.out.print(myIntArray[0]);
//prints 0
//myIntArray and array2 “refer” to the
same array