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Outputting primitive values as strings


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Java Essential Training

with David Gassner
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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

Video: Outputting primitive values as strings

No matter what kind of value you are working within Java, you can typically output that value as a string, simply by concatenating it to some other value. To demonstrate this, I have declared eight variables, one each of the primitive data types, character, Boolean, byte and so on. Each of these is using a literal value as its initial value. Now I'll place the cursor after the declarations and use System.out.println and first I'll output the character. I'll save and run the application and I get the letter z, that's pretty expected.

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Java Essential Training
7h 17m Beginner Dec 14, 2011

Viewers: in countries Watching now:

Join author David Gassner as he explores Java SE (Standard Edition), the language used to build mobile apps for Android devices, enterprise server applications, and more. This course demonstrates how to install both Java and the Eclipse IDE and dives into the particulars of programming. The course also explains the fundamentals of Java, from creating simple variables, assigning values, and declaring methods to working with strings, arrays, and subclasses; reading and writing to text files; and implementing object oriented programming concepts.

Topics include:
  • Understanding the history and principles of Java
  • Installing Eclipse and Java
  • Compiling and running from the command line
  • Managing memory and performing garbage collection
  • Declaring and initializing variables
  • Writing conditional code
  • Building and parsing strings
  • Debugging and exception handling
  • Using simple arrays
  • Creating custom classes
  • Working with encapsulation, inheritance, and polymorphism
  • Managing files
  • Documenting code with Javadocs
Subjects:
Developer Programming Languages
Software:
Android Java Eclipse
Author:
David Gassner

Outputting primitive values as strings

No matter what kind of value you are working within Java, you can typically output that value as a string, simply by concatenating it to some other value. To demonstrate this, I have declared eight variables, one each of the primitive data types, character, Boolean, byte and so on. Each of these is using a literal value as its initial value. Now I'll place the cursor after the declarations and use System.out.println and first I'll output the character. I'll save and run the application and I get the letter z, that's pretty expected.

Now one of the great things that Java does for you is that when you want to translate something into a string, it's usually fairly automatic. I am going to copy and then paste this line seven times and I'll change the values that I am outputting in each of these lines using the Boolean, the byte, the short, the integer, the long, the float, and the double. I'll save and run the application again and there is the result. Notice that all the values are output almost exactly as they were set. The one exception is the double which had so many digits before the decimal that Java automatically translated it for me.

When you output values using the out object's print or println commands, these are usually automatically translated to strings. But the same translation happens whenever you concatenate values. Let' take one of these values, the short and I am going to output the short value, concatenate it to a string. I'll use System.out.println ("The value of s is -- and then I'll use the plus operator and the value s. I'll save the changes and run the application and I get what you would expect, The value of s is 32000.

Now, in some languages, it matters when you are concatenating whether the first value is a string or whether the first value is a number. In some languages, if the first value is a number, then the plus operator will be used for math, but if the first value is a string then it will be used for concatenation. So let's test that in Java. I'll take this println command and copy and paste it and I'll reverse the order. Instead of starting with the string, I'll start with the numeric value, s + " is the value of s. In some languages, this would cause an error because the first value was a number and the plus operator should be seen as a mathematical plus rather than as a string concatenation plus, but in Java, the rule is that if there is even one string involved then the whole thing will be turned into a string.

I'll run the application and I'll see that that works as well. You can also combine math and string concatenation. If an expression starts with a mathematical operation, such as 2+2, the math will be executed first. The result will then be converted to a string and concatenated to the rest of the expression. If you put the math at the end of the expression though, everything will be treated as a string. Finally, complex objects are also translated to strings automatically. If you declare a string and then output a string, that's pretty simple.

You are just getting the value of the string object, but what about dates. I'll create a new Date object. I'll use the Date class and a variable name of myDate = new Date and then I'll use System.out.println ("The new date is -- and then I'll output myDate. If you see any errors, that means that you have to include a special notation at the top of the screen called a package. The Date class is member of a package that has to be explicitly imported.

I'll talk about class importing later, but for now, all you need to do is place the cursor after the data type Date and press Ctrl+Space. Then, choose this version of the Date class, Date in java.util, double click it and at the top of the screen, you'll see a statement added import java.util.date. That's an instruction to the compiler that says, when I refer to the Date class, this is the version I mean. Now I'll save my changes and run the application and I get a long string, the string representation of the current date and time.

So how is this happening? Well, every complex class in Java has a special method called toString. Let's look at the documentation for the Date class. I'll double-click date and then go to Dynamic Help. I'll click on Javadoc for java.util. date and maximize that screen, I'll click the Method list, scroll down and here is the toString method. Every class has this toString method and the implementation of the method is going to be different from one class to another.

When you pass a complex object into System.out.println or otherwise concatenate the object to an existing string, Java automatically looks for this method, toString, executes it, takes the return value, and that's what will become a part of the string. You'll see in later videos when you create your own complex classes that you can use this model pretty effectively for debugging and other tools in your application. When you create your own custom classes and you give them a toString method, you will be able to take instances of those classes, pass them into these methods that require strings and the translation will happen automatically.

So that's a look at how values are translated from their native data types into strings in Java. Again, primitives translate automatically, but complex objects depend on the toString method which is implemented differently for each class.

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