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Working with boolean values

From: Java Essential Training

Video: Working with boolean values

True and false values are stored in Boolean variables in Java. You can either use primitive data types or the matching wrapper class also spelled Boolean with an uppercase B. I am working in a project named Booleans which you can find in Chapter 04 of the Exercise Files. I'll declare two variables. For primitive data types, use the keyword boolean, all lowercase. My first variable will be names b1 and will have a value of true. The second variable will be b2 and it will have a value of false.

Working with boolean values

True and false values are stored in Boolean variables in Java. You can either use primitive data types or the matching wrapper class also spelled Boolean with an uppercase B. I am working in a project named Booleans which you can find in Chapter 04 of the Exercise Files. I'll declare two variables. For primitive data types, use the keyword boolean, all lowercase. My first variable will be names b1 and will have a value of true. The second variable will be b2 and it will have a value of false.

These are the only two possible literal values for Booleans variables. Unlike in many languages such as JavaScript, you can't just replace the Boolean keywords true and false with say numeric values. There is no built-in logic that says 0 is false and any other number is true. So you have to use the words true or false. They are spelled in all lowercase and don't get any quotes or other notation. If you try to output these values to the console, they will be translated as their equivalent strings. So I'll add this code System.out.println (" The value of b1 is-- and then I'll append b1.

Then I'll make a copy of that and paste it and I'll run the application and I'll see that the value of b1 is true and the value of b2 is false. You can reverse the value of a Boolean variable by prepending the exclamation mark or bang symbol. So for example I'll create a new variable. I'll call it b3 and I'll use the reverse value of b1 using !b1. Then I'll make a copy of my println command and I'll paste it in.

I'll change to the b3 variable and I'll run the application and I see that the result of reversing b1 which started as true is now false. If you want to evaluate numbers as Booleans, you have to write the code yourself, but it's actually a pretty small amount of code. Let's create an integer value named i and set it to a value of 1. Now again in many languages the #1 would have an equivalent value of true, but that equivalents doesn't exist already in Java, so we have to code it. So I'll create a variable named boolean b4 and I'll use this logic.

I'll create a pair of parenthesis and in there I'll use the expression, i != 0. So the expression comparing the value of the integer to the value 0 is wrapped inside parenthesis that forces it to be evaluated first and then the Boolean result which results from asking the question do these values match is returned to my boolean variable. Then I'll once again use a println command, I'll put the value of b4 and because i does not equal 0, I should get a value of true.

If I change the value of int i to 0 then the value of b4 is false. So this simple expression is a very easy way to take care of the situation where you want to translate a numeric value to a Boolean value. Finally, just as with the other primitive data types there is a wrapper class. It's named Boolean with an uppercase B and as with all the data type wrapper classes, it's a member of the package java.lang which means it always available to your code. The Boolean class has a fairly small set of supporting methods.

I'll show you how to use this one, parseBoolean. The parseBoolean method accepts a String value and translates it into a real Boolean. So let's go back to Eclipse and at the bottom of the code, I am going to declare a String, I'll just name is s and I'll give a value of true. Then I'll create a boolean variable, I'll call it b5 and I'll call that parsing method from the Boolean class, Boolean. parseBoolean and I'll pass in the value of s. And finally, I'll once again copy and paste System.out.println and change to output the value of b5 and show you that the result is a value of true.

Now the logic that's going on here is pretty interesting. The parseBoolean method is non-case sensitive. So I can actually spell the word true with upper or lower case characters, even though the true keyword in Java is all lowercase. I'll make that change and show you that evaluation still returns true. And if I change the value of s2, false, either upper or lowercase, I'll get the value false, so far as expected. But what happens if you pass in a value that's neither true nor false? I'll pass in xyz.

When I run the application now, I don't get an error. Instead, I get back a value of false. The logic that this method is using is if it's not true then it must be false. So any version of the word true will return true and any other string will return false. So that's a look at some of the rules around Booleans in Java. Once again, you start off with the keywords true and false which are the only available literals for a Boolean variable. You can reverse a Boolean variable, using the != operator and you can use the Boolean wrapper class to parse strings as Booleans and accomplish other tasks that are common to true and false values.

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This video is part of

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Java Essential Training

71 video lessons · 69576 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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