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When declaring an array reference variable, the square brackets [] may appearas part of the type, or following the variable name, or both.
Once an array object is created, its type and length never changes.
An array object is created by an array creation expression or an array initializer.
An array creation expression (or an array initializer) specifies:
The length of the array is always available as a final instance variable named length .
An array element is accessed by an expression whose value is an array reference followed by an indexing expression enclosed by matching squarebrackets.
If an attempt is made to access the array with an invalid index value, an ArrayIndexOutOfBoundsException will be thrown.
Arrays must be indexed by integer values of the types int , short , byte , or char . An array cannot be accessed using an index of type long .
If the elements in an array are not purposely initialized when the array is created, the array elements will be automatically initialized with defaultvalues.
The values in the array elements may be purposely initialized when the array object is created using a comma-separated list of expressions enclosed bymatching curly brackets.
The program in this module illustrated three different ways to emulate traditional rectangular two-dimensional arrays.
The program also illustrated two different ways to create and work with ragged arrays.
In the next module, I will provide so additional information about array objects, and then illustrate the use of the classes named Array and Arrays for the creation and manipulation of array objects.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
A complete listing of the program is shown in Listing 26 below.
| Listing 26 . Complete program listing. |
|---|
/*File Array07.java
Copyright 2002, R.G.BaldwinThis program illustrates three
different ways to emulate a traditionalrectangular array in Java. Two of
those ways are essentially raggedarrays with equal-length sub arrays.
The program also illustrates two waysto create ragged arrays in Java.
Tested using JDK 1.3 under Win 2000.**************************************/
public class Array07{public static void main(
String[]args){
//Create an array structure that// emulates a traditional
// rectangular array with two rows// and three columns. This
// approach requires all rows to// be the same length.
Object[][] v1 = new Object[2][3];//Populate the array elements with
// references to objects of type// Integer.
for(int i=0;i<v1.length;i++){
for(int j=0;j<v1[i].length;j++){v1[i][j]=
new Integer((i+1)*(j+1));}//end inner loop
}//end outer loop//Display the array elements
for(int i=0;i<v1.length;i++){
for(int j=0;j<v1[i].length;j++){System.out.print(
v1[i][j] + " ");}//end inner loop
System.out.println();//new line}//end outer loop
System.out.println();//new line//Create a ragged array with two
// rows. The first row has three// columns and the second row has
// three columns. The length of// each row could be anything, but
// was set to three to match the// above array structure.
Object[][] v2 = new Object[2][];v2[0] = new Object[3];
v2[1]= new Object[3];//Populate the array elements with
// references to objects of type// Integer.
for(int i=0;i<v2.length;i++){
for(int j=0;j<v2[i].length;j++){
v2[i][j] =new Integer((i+1)*(j+1));
}//end inner loop}//end outer loop
//Display the array elementsfor(int i=0;i<v2.length;i++){
for(int j=0;j<v2[i].length;j++){System.out.print(
v2[i][j] + " ");}//end inner loop
System.out.println();//new line}//end outer loop
System.out.println();//new line//Create a one-dimensional array
// of type Object, which contains// references to array objects of
// type Object. The secondary// array objects could be of any
// length, but were set to three// to match the above array
// structure.Object[] v3 = new Object[2];
v3[0]= new Object[3];v3[1] = new Object[3];
//Populate the array elements with// references to objects of type
// Integer.for(int i=0;i<v3.length;i++){
for(int j=0;j<((Object[])v3[i]).length;
j++){((Object[])v3[i])[j] =new Integer((i+1)*(j+1));
}//end inner loop}//end outer loop
//Display the array elementsfor(int i=0;i<v3.length;i++){
for(int j=0;j<((Object[])v3[i]).length;
j++){System.out.print(
((Object[])v3[i])[j]+ " ");
}//end inner loopSystem.out.println();//new line
}//end outer loopSystem.out.println();//new line
//Create a ragged array with two// rows. The first row has two
// columns and the second row has// three columns.
Object[][] v4 = new Object[2][];v4[0] = new Object[2];
v4[1]= new Object[3];//Populate the array elements with
// references to objects of type// Integer.
for(int i=0;i<v4.length;i++){
for(int j=0;j<v4[i].length;j++){v4[i][j]=
new Integer((i+1)*(j+1));}//end inner loop
}//end outer loop//Display the array elements
for(int i=0;i<v4.length;i++){
for(int j=0;j<v4[i].length;j++){System.out.print(
v4[i][j] + " ");}//end inner loop
System.out.println();//new line}//end outer loop
System.out.println();//new line//Create a one-dimensional array
// of type Object, which contains// references to array objects of
// type Object. The secondary// array objects could be of any
// length, but were set to two and// three to match the ragged array
// above.Object[] v5 = new Object[2];
v5[0]= new Object[2];v5[1] = new Object[3];
//Populate the array elements with// references to objects of type
// Integer.for(int i=0;i<v5.length;i++){
for(int j=0;j<((Object[])v5[i]).length;
j++){((Object[])v5[i])[j] =new Integer((i+1)*(j+1));
}//end inner loop}//end outer loop
//Display the array elementsfor(int i=0;i<v5.length;i++){
for(int j=0;j<((Object[])v5[i]).length;
j++){System.out.print(
((Object[])v5[i])[j]+ " ");
}//end inner loopSystem.out.println();//new line
}//end outer loopSystem.out.println();
//Create a one-dimensional array// of type int, which contains
// references to array objects of// type Object. The secondary
// array objects could be of any// length.
Object[]v6 = new Object[2];v6[0] = new int[7];
v6[1]= new int[3];//Now illustrate that the elements
// of the leaves of a ragged array// implemented in this manner can
// contain primitive values.// Populate the array elements with
// type int.for(int i=0;i<v6.length;i++){
for(int j=0;j<((int[])v6[i]).length;
j++){((int[])v6[i])[j] = (i+2)*(j+2);}//end inner loop
}//end outer loop//Display the array elements
for(int i=0;i<v6.length;i++){
for(int j=0;j<((int[])v6[i]).length;
j++){System.out.print(
((int[])v6[i])[j]+ " ");
}//end inner loopSystem.out.println();//new line
}//end outer loop}//end main
}//end class Array07 |
-end-
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