{"id":68889,"date":"2022-11-24T09:00:42","date_gmt":"2022-11-24T09:00:42","guid":{"rendered":"https:\/\/www.cryptocabaret.com\/?p=68889"},"modified":"2022-11-24T09:00:42","modified_gmt":"2022-11-24T09:00:42","slug":"use-arrays-in-java","status":"publish","type":"post","link":"https:\/\/www.cryptocabaret.com\/?p=68889","title":{"rendered":"Use arrays in Java"},"content":{"rendered":"

Use arrays in Java<\/span>
\nSeth Kenlon<\/a><\/span>
\nThu, 11\/24\/2022 – 03:00<\/span><\/p>\n

\n

In the Java programming language, an array is an ordered collection of data. You can use an array to store information in a structured way. It’s useful to know the various ways you can retrieve that data when you need it. It’s worth noting that in Java, an associative array (also called a dictionary in some languages) is called a hashmap. This article doesn’t cover hashmaps, but you can read all about them in my Using a hashmap in Java<\/a> article.<\/p>\n

Creating a string array<\/h2>\n

The simplest array in Java is a one-dimensional array. It’s essentially a list. For an array of strings:<\/p>\n

\n
package<\/span> com.opensource.example<\/span>;<\/span>

public<\/span> class<\/span> Example {<\/span>

\n\u00a0 \u00a0 public<\/span> static<\/span> void<\/span> main(<\/span>String<\/span><\/a>[<\/span>]<\/span> args)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 String<\/span><\/a>[<\/span>]<\/span> myArray =<\/span> {<\/span>\"foo\"<\/span>, \"bar\"<\/span>, \"baz\"<\/span>}<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 \/\/ retrieval<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>0<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>1<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>2<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/div><\/div><\/pre>\n
Notice that when you retrieve the data from an array, the index starts at 0, not 1. In other words, an array containing three values is numbered 0 to 2.<\/p>\n
Alternatively, you can create an array and populate it later. When you do this, however, you must also tell Java the length of the array. The “length”, in this context, refers to the number of items an array can hold.<\/p>\n
\n
package<\/span> com.opensource.example<\/span>;<\/span>

public<\/span> class<\/span> Example {<\/span>
\n\u00a0 \u00a0 public<\/span> static<\/span> void<\/span> main(<\/span>String<\/span><\/a>[<\/span>]<\/span> args)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 String<\/span><\/a>[<\/span>]<\/span> myArray =<\/span> new<\/span> String<\/span><\/a>[<\/span>3<\/span>]<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>\"Empty myArray created.\"<\/span>)<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 \/\/ populate the array<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 myArray[<\/span>0<\/span>]<\/span> =<\/span> \"foo\"<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 myArray[<\/span>1<\/span>]<\/span> =<\/span> \"bar\"<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 myArray[<\/span>2<\/span>]<\/span> =<\/span> \"baz\"<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 \/\/ retrieval<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>0<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>1<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>2<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/div><\/div><\/pre>\n
Assuming the code is saved in a file called main.java<\/code>, run it using the java<\/code> command:<\/p>\n
\n
$ java<\/span> .\/<\/span>main.java
\nfoo
\nbar
\nbaz<\/div><\/div><\/pre>\n
To create an array of integers, define the data type as int<\/code> instead of String<\/code>:<\/p>\n
\n
package<\/span> com.opensource.example<\/span>;<\/span>

public<\/span> class<\/span> Example {<\/span>
\n\u00a0 \u00a0 public<\/span> static<\/span> void<\/span> main(<\/span>String<\/span><\/a>[<\/span>]<\/span> args)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 int<\/span>[<\/span>]<\/span> myArray =<\/span> {<\/span> 1<\/span>, 2<\/span>, 3<\/span> }<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>0<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>1<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>2<\/span>]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/div><\/div><\/pre>\n
Run the code:<\/p>\n
\n
$ java<\/span> .\/<\/span>main.java
1<\/span>
2<\/span>
3<\/span><\/div><\/div><\/pre>\n<\/p>\n
\n
More on Java<\/div>\n
\n
What is enterprise Java programming?<\/a><\/div>\n
An open source alternative to Oracle JDK<\/a><\/div>\n
Java cheat sheet<\/a><\/div>\n
Red Hat build of OpenJDK<\/a><\/div>\n
Free online course: Developing cloud-native applications with microservices<\/a><\/div>\n
Fresh Java articles<\/a><\/div>\n<\/p><\/div>\n<\/p><\/div>\n
Iterating over an array<\/h2>\n
Once you’ve stored data in an array, you probably intend to retrieve it at some point. The most direct way to see all data in an array is to create a for<\/code> loop that gets the length of the array using the .length<\/code> method, and then loops over the array a number of times equal to the length:<\/p>\n
\n
package<\/span> com.opensource.example<\/span>;<\/span>

public<\/span> class<\/span> Example {<\/span>
\n\u00a0 \u00a0 public<\/span> static<\/span> void<\/span> main(<\/span>String<\/span><\/a>[<\/span>]<\/span> args)<\/span> {<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 String<\/span><\/a>[<\/span>]<\/span> myArray =<\/span> {<\/span> \"foo\"<\/span>, \"bar\"<\/span>, \"baz\"<\/span> }<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 \u00a0 for<\/span> (<\/span>int<\/span> i=<\/span>0<\/span>;<\/span> i  myArray.length<\/span>;<\/span> i++<\/span>)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>i]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 }<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/span><\/div><\/div><\/pre>\n
Run the code:<\/p>\n
\n
$ java<\/span> .\/<\/span>main.java
\nfoo
\nbar
\nbaz<\/div><\/div><\/pre>\n
Multidimensional arrays<\/h2>\n
An array doesn’t have to be just a simple list. It can also be a list of lists. This is called a multidimensional array, and it’s pretty intuitive as long as you think of it as an array of arrays:<\/p>\n
\n
package<\/span> com.opensource.example<\/span>;<\/span>

public<\/span> class<\/span> Example {<\/span>
\n\u00a0 \u00a0 public<\/span> static<\/span> void<\/span> main(<\/span>String<\/span><\/a>[<\/span>]<\/span> args)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 String<\/span><\/a>[<\/span>]<\/span>[<\/span>]<\/span> myArray =<\/span> {<\/span>{<\/span> \"zombie\"<\/span>, \"apocalypse\"<\/span> }<\/span>, {<\/span> \"happy\"<\/span>, \"halloween\"<\/span> }<\/span>}<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 }<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/div><\/div><\/pre>\n
To see the contents of the array, you can use a nested for<\/code> loop. In a one-dimensional array, you had to obtain the length of myArray<\/code> so your for<\/code> loop knew when to stop iterating over the array. This time, you must obtain the length of each array within myArray<\/code>. For simplicity, I call these two arrays outer<\/code> and inner<\/code>, with the former being myArray<\/code>, and the inner<\/code> representing each nested array:<\/p>\n
\n
int<\/span> outer =<\/span> myArray.length<\/span>;<\/span>
int<\/span> inner =<\/span> myArray[<\/span>1<\/span>]<\/span>.length<\/span>;<\/span><\/div><\/div><\/pre>\n
Once you have both lengths, you use them as the limits of your for<\/code> loop:<\/p>\n
\n
for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i  outer;<\/span> i++<\/span>)<\/span> {<\/span>
\n\u00a0 for<\/span> (<\/span>int<\/span> j =<\/span> 0<\/span>;<\/span> j  inner;<\/span> j++<\/span>)<\/span> {<\/span>
\n\u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>i]<\/span>[<\/span>j]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 }<\/span>
\n\u00a0 }<\/span><\/span><\/span><\/div><\/div><\/pre>\n
Here’s the full code sample:<\/p>\n
\n
package<\/span> com.opensource.example<\/span>;<\/span>

\n\u00a0 public<\/span> class<\/span> Example {<\/span>
\n\u00a0 \u00a0 \u00a0 String<\/span><\/a>[<\/span>]<\/span>[<\/span>]<\/span> myArray =<\/span> {<\/span>{<\/span> \"foo\"<\/span>, \"bar\"<\/span> }<\/span>, {<\/span> \"baz\"<\/span>, \"qux\"<\/span> }<\/span>}<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 int<\/span> outer =<\/span> myArray.length<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 int<\/span> inner =<\/span> myArray[<\/span>1<\/span>]<\/span>.length<\/span>;<\/span>

\n\u00a0 \u00a0 \u00a0 for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i  outer;<\/span> i++<\/span>)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0for<\/span> (<\/span>int<\/span> j =<\/span> 0<\/span>;<\/span> j  inner;<\/span> j++<\/span>)<\/span> {<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 System<\/span><\/a>.out<\/span>.println<\/span>(<\/span>myArray[<\/span>i]<\/span>[<\/span>j]<\/span>)<\/span>;<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 }<\/span>
\n\u00a0 \u00a0 \u00a0 \u00a0 }<\/span>
\n\u00a0 \u00a0 }<\/span>
}<\/span><\/span><\/span><\/div><\/div><\/pre>\n
Run the code:<\/p>\n
\n
$ java<\/span> .\/<\/span>main.java
\nzombie
\napocalypse
\nhappy
\nhalloween<\/div><\/div><\/pre>\n
Arrays of data<\/h2>\n
Sometimes it makes more sense to use a Java array than to track dozens of individual variables. Once you understand how to structure and retrieve data in a language, you can generate complex data in an organized and convenient way.<\/p>\n<\/div>\n
\n
Instead of tracking dozens of individual variables, use an array in Java to collect and store data in a structured way.<\/p>\n<\/div>\n
\n
\n
  \"What<\/div>\n
Image by: <\/span><\/p>\n
Pixabay. CC0.<\/p>\n<\/div>\n<\/article>\n<\/div>\n
\n
Programming<\/a><\/div>\n
Java<\/a><\/div>\n<\/p><\/div>\n
What to read next<\/div>\n

\n        \"Creative<\/a>This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.<\/div>\n
\n
\n
Register<\/a> or Login<\/a> to post a comment.<\/div>\n<\/p><\/div>\n<\/section>\n
Powered by WPeMatico<\/a><\/small><\/p>\n","protected":false},"excerpt":{"rendered":"
Use arrays in Java Seth Kenlon Thu, 11\/24\/2022 – 03:00 In the Java programming language, an array is an ordered collection of data. You can use an array to store information in a structured way. It’s useful to know the various ways you can retrieve that data when you need it. It’s worth noting that […]<\/p>\n","protected":false},"author":1,"featured_media":68890,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[307],"tags":[],"class_list":["post-68889","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-open-source"],"_links":{"self":[{"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/posts\/68889","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=68889"}],"version-history":[{"count":0,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/posts\/68889\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=\/wp\/v2\/media\/68890"}],"wp:attachment":[{"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=68889"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=68889"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cryptocabaret.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=68889"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}