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Building strings with StringBuilder

From: Java Essential Training

Video: Building strings with StringBuilder

The string class is one of the most common complex classes you'll use in Java. The string class has a special characteristic, it's immutable. This means that when you set a value of a string object that value cannot be changed. Now it might seem like you can change it. Let's take some very simple code, I have declared a string called s1 and given it a value of Welcome, I'll place the cursor on the next line and say s1 = s1+ "to California!"; you could also write this code using the += operator, either way it looks like you're appending to an existing value and simply changing the value of an existing variable.

Building strings with StringBuilder

The string class is one of the most common complex classes you'll use in Java. The string class has a special characteristic, it's immutable. This means that when you set a value of a string object that value cannot be changed. Now it might seem like you can change it. Let's take some very simple code, I have declared a string called s1 and given it a value of Welcome, I'll place the cursor on the next line and say s1 = s1+ "to California!"; you could also write this code using the += operator, either way it looks like you're appending to an existing value and simply changing the value of an existing variable.

Then I'll output the value of that variable to the screen using System.out.println, and I'll parse in s1 and I'll Run the application and everything looks like it's working just fine, but it's not so great in the background. What's really happening is that when you append a value or otherwise change the value of the string variable, you're actually creating a new instance of the string class, and you're abandoning the reference to the old object. That old object is still out there in memory; it becomes eligible for garbage collection.

But in fact, you're using more memory than you need to or should. You won't see this behaviorally in your applications, the issue only becomes apparent when you're trying to tune your applications in a small memory environment, or you're working with very large scale applications. But because this is a universal issue in Java, it's good to know how to deal with it from the beginning. Java provides two utility classes called StringBuffer and StringBuilder, these two classes have the same API or programming interface, and they both implement the same methods named insert and append.

The insert method can be used to insert text into a string at either the beginning or any other position in the string. And the append method can be used to append text to a string. You can use either the StringBuilder or the StringBuffer in most environments, but in general, the StringBuilder is more slender, it takes less memory and resources, but it's only good for single threaded environments. StringBuffer should be used where you need to synchronize the use of a string among multiple threads. If you're new to Java don't worry about it, just use StringBuilder until you find out you have to StringBuffer.

So here is an example of how you might use StringBuilder. I'm going to take this little bit of code out and leave myself with the simple s1 variable and then after I've created the initial string, I'll create another variable named StringBuilder, notice that StringBuilder and StringBuffer are both members of the package java.lang, so they're always available to your code. So I'll declare the variable StringBuilder and I'll name sb and I'll instantiate it using new StringBuilder, I'll place the cursor inside the parentheses and press Ctrl+Space and show you the different ways that you can create a StringBuilder.

You can either call the constructor method with no arguments or with some of these other settings, but the one I'm going to use is an initial string and I'll parse in s1. So now my StringBuilder class is being created and it's been populated with that initial value. Now to append a value, I'll call sb. append and I'll parse in that appended value that I used before, "to California!" and I'll change my print line command to output sb, the StringBuilder. I'll Run the application and I get the same result.

Whenever you're working with strings that you need to manipulate, either adding text or inserting text, use the StringBuilder class instead of a simple string, you'll create fewer objects and you'll conserve memory.

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This video is part of

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Java Essential Training

71 video lessons · 71666 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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