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Using simple arrays

From: Java Essential Training

Video: Using simple arrays

Java gives you a couple of ways of managing ordered collections of data in memory. The simplest approach syntactically is to use simple arrays. Simple arrays are very easy to code, but they're not particularly flexible. There are couple things to know about simple arrays. First all of the items in an array must be of the same type, so you can create an array of integers or create an array of strings, but you can't create an array that contains both. Also, when you declare an array it's always of a fixed size. You set the size when you declare it and you can't change the size at runtime.

Using simple arrays

Java gives you a couple of ways of managing ordered collections of data in memory. The simplest approach syntactically is to use simple arrays. Simple arrays are very easy to code, but they're not particularly flexible. There are couple things to know about simple arrays. First all of the items in an array must be of the same type, so you can create an array of integers or create an array of strings, but you can't create an array that contains both. Also, when you declare an array it's always of a fixed size. You set the size when you declare it and you can't change the size at runtime.

If you want to use resizable arrays you want to take a look at the class array list which I'll describe in a separate video. There are few different syntax styles that you can use to declare and initialize an array. I'm working in an empty main method in a project named simple arrays. Here is one style of syntax. Start with the data type of the array, followed by a pair of brackets, then assign, the array name, put in an equals operator, and then initialize the array using the new keyword, the data type again and the brackets again but this time the size.

So this is an array of three integers. Now, I'll add up a little bit of looping code. I'll type in for and press Ctrl+ Spacebar and I'll choose iterate over array, I'm iterating over the a1 array, Eclipse figured that out for me. And within the for loop I'll output System.out.println and I'll output the value of a1, bracket, i, bracket) meaning the item at position i. I'll save and run the application and the output is three zeros.

Now, there is a variation on this syntax that's possible and it's completely a matter of preference which one you use. I am going to select and copy this block of code and then paste it in. I'll change the name of the second array to a2. I'll make the change in three places, here, here and here. And then I'm going to take the brackets and move them from after the data type and paste them after the array name. This variation does exactly the same thing as the first version. It creates an array of three items and the items will have their default value.

Integer is just like all other primitive numeric types, have the default value of zero. And so when I print these out once again I should get three zeros, and when I run the application, I get the three items in array a1 and the three items in array a2. The third style syntax for simple arrays is to initialize the values in the declaration statement. I've used this version of the syntax previously in the course. Start off with your data type, once again you can place the brackets either after the data type or after the array name and then put in a pair of curly braces and then declare your list of items as a comma delimited list.

So I'll add in a list of 3, 6, 9. The number of items in the array and their values are determined by that list. As with the previous declarations, once the array is set to have a particular number of items it will always have that number of items, you can't change it at runtime. I'll make a copy of one of these for loops, and I'll copy and paste it down here. I'll change the references here from a2 to a3. I'll run the application and there is the result.

The last array has values of 3, 6 and 9. Once you've declared an array, you can address the items in the array using array syntax, where you referred to the index of an item using zero-based numbering wrapped inside brackets. So for example, I could say System.out. println, "The value of the first item is" and then I can address a3, open bracket, 0.

I'll save and run the application, and I see that the value of the first item is three. And as I've shown in previous videos, if I try to address an array item and I get it wrong, if I put in an index to an item that does not exist I'll generate an exception a runtime error. So that's the basics of simple arrays, once again the syntax can vary a little bit, you can place these initial brackets either after the data type or after the array name and you can either use the new keyword and an explicit number of items in the array, or you can use a comma delimited list wrapped in braces.

Either way the array must contain items all of the same data type and it is not resizable at runtime.

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This video is part of

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Java Essential Training

71 video lessons · 72224 viewers

David Gassner
Author

 
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  1. 10m 8s
    1. Welcome
      1m 3s
    2. Is this course for you?
      5m 35s
    3. Using the exercise files
      3m 30s
  2. 31m 24s
    1. The history of Java
      5m 19s
    2. Java compilation and syntax
      8m 54s
    3. Understanding the principles of Java
      8m 28s
    4. Choosing a development environment
      8m 43s
  3. 19m 5s
    1. Installing Java on Windows
      6m 42s
    2. Installing Eclipse on Windows
      3m 19s
    3. Exploring Java on Mac OS X Leopard and Snow Leopard
      2m 27s
    4. Installing Java on Mac OS X Lion
      3m 27s
    5. Installing Eclipse on Mac OS X
      3m 10s
  4. 46m 10s
    1. Creating a Hello World application
      11m 7s
    2. Exploring the Eclipse IDE
      8m 55s
    3. Compiling and running from the command line
      8m 2s
    4. Passing arguments to the application
      8m 17s
    5. Using the Java API documentation
      4m 5s
    6. Memory management and garbage collection
      5m 44s
  5. 58m 57s
    1. Everything is an object
      5m 59s
    2. Declaring and initializing variables
      9m 15s
    3. Working with numbers
      8m 32s
    4. Converting numeric values
      6m 40s
    5. Understanding operators
      7m 58s
    6. Working with character values
      5m 14s
    7. Working with boolean values
      5m 13s
    8. Outputting primitive values as strings
      5m 33s
    9. Creating a simple calculator application
      4m 33s
  6. 53m 40s
    1. Writing conditional code
      5m 35s
    2. Using the switch statement
      8m 50s
    3. Repeating code blocks with loops
      7m 35s
    4. Creating reusable code with methods
      6m 31s
    5. Declaring methods with arguments
      5m 41s
    6. Overloading method names with different signatures
      5m 53s
    7. Passing arguments by reference or by value
      5m 35s
    8. Creating a more complex calculator application
      8m 0s
  7. 20m 30s
    1. Using the String class
      5m 44s
    2. Building strings with StringBuilder
      3m 34s
    3. Parsing string values
      3m 19s
    4. Working with date values
      7m 53s
  8. 20m 44s
    1. Understanding compile-time vs. runtime errors
      4m 5s
    2. Handling exceptions with try/catch
      4m 55s
    3. Throwing exceptions in methods
      2m 50s
    4. Using the debugger
      8m 54s
  9. 32m 22s
    1. Using simple arrays
      4m 47s
    2. Using two-dimensional arrays
      6m 17s
    3. Managing resizable arrays with ArrayList
      7m 14s
    4. Managing unordered data with HashMap
      6m 5s
    5. Looping through collections with iterators
      7m 59s
  10. 52m 2s
    1. Understanding encapsulation
      5m 59s
    2. Creating and instantiating custom classes
      8m 8s
    3. Organizing classes with packages
      6m 47s
    4. Creating and using instance methods
      6m 52s
    5. Storing data in instance variables
      6m 56s
    6. Using constructor methods
      5m 40s
    7. Managing instance data with getter and setter methods
      8m 26s
    8. Using class variables and Enum classes
      3m 14s
  11. 41m 15s
    1. Understanding inheritance and polymorphism
      9m 12s
    2. Extending custom classes
      9m 1s
    3. Overriding superclass methods
      3m 8s
    4. Casting subclass objects
      5m 3s
    5. Understanding interfaces and implementing classes
      4m 2s
    6. Creating your own interfaces
      4m 14s
    7. Using abstract classes and methods
      6m 35s
  12. 32m 17s
    1. Managing files with the core class library
      7m 46s
    2. Managing files with Apache Commons FileUtils
      7m 32s
    3. Reading a text file from a networked resource
      7m 52s
    4. Parsing an XML file with DOM
      9m 7s
  13. 17m 39s
    1. Creating your own JAR files
      4m 54s
    2. Understanding the classpath
      5m 2s
    3. Documenting code with Javadoc
      7m 43s
  14. 47s
    1. Goodbye
      47s

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