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Using the String class


Java Essential Training (2011)

with David Gassner

Video: Using the String class

Using the String class provides you with in-depth training on Developer. Taught by David Gassner as part of the Java Essential Training (2011)
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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 25s
    1. The history of Java
      5m 19s
    2. Understanding the principles of Java
      8m 28s
    3. Java compilation and syntax
      8m 55s
    4. Choosing a development environment
      8m 43s
  3. 19m 52s
    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
      4m 14s
    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 41s
    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 42s
    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 31s
    1. Using the String class
      5m 44s
    2. Building strings with StringBuilder
      3m 34s
    3. Parsing string values
      3m 20s
    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 3s
    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 15s
  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

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Watch the Online Video Course Java Essential Training (2011)
Video Duration: 5m 44s7h 17m Beginner Dec 14, 2011

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View Course Description

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
Android Java Eclipse
David Gassner

Using the String class

The string class is one of the most commonly used complex types in Java. I call it a complex type, because when you create a string, you're creating an instance of a class. It's not a primitive variable, such as char, int, short and the others. I'm working in a project called strings that's part of the Chapter 6 Exercise Files. And the beginning class just has an empty main method. I'll start by declaring a string named s1 and I'll give it a value of "Welcome to California!" When you declare a literal string in Java, you must wrap the string in double quotes; single quotes are only used for character types.

Double quotes are always used for strings. Now I'll output the value to the console using System.out.println(s1). I'll run the application and predictably I get the output "Welcome to California!" Now you can declare strings in one of two ways. This syntax where you assign a literal string directly to the equals assignment operator is actually a shortcut. Because the string class is a complex class, you are actually creating an instance of the class. And you can also use the more conventional instantiation syntax.

It would look like this, I'll declare a second string named s2, I'll use the new keyword, I'll call the constructor method for the string class. A constructor method is a method of a class that has the same name as the class itself, and then I'm going to pass in exactly the same value to the constructor method. I'll select that text including the quotes and paste it between the parentheses and then add the semicolon at the end. And I'll change the variable that I'm outputting from s1 to s2, I'll Save and Run and the output is exactly the same.

You can use either syntax style to create a string, they are functionally equivalent. Now I mentioned in an earlier video that if you want to compare two string values, you shouldn't use the double equals operator. It's unpredictable. There are some circumstances in which you can compare s1 and s2, and if they have the same value, you'll get a true value back and there are some situations where you won't. This is a situation where you won't. If you declare one string using the shorthand syntax with the equals assignment operator and just a literal string, and the second string using the constructor method, then you can't compare the values using double equals.

It's a strange situation, but I want to show you the result. I'll place the cursor at the end of the existing code and I'll create a conditional block. I'll type if and press Ctrl+Space, choose the if statement, and then I'll set my condition as s1 has a value of s2, using the double equals operator. And then in the conditional block, I'll use System.out.println and I'll output the string, ("They match!"). I'll add an else clause and I'll make a copy of this println command, paste it into the else clause and change that to ("They don't match!").

I'll Run the application and I get back a negative result even though those two values look like they match pretty closely. So here's what's going on, the s1 and s2 objects are different objects. Even though they have the same string value, you can't reliably use the double equals operator this way. So instead, you should use a method called equals. The string class has a very deprogramming interface and the equals method is one of its most useful methods. Let's take a look at the documentation for the string class, I'll double-click the data type string, go to Dynamic Help on the Help menu, click the link for the class Java.lang.string and maximize the help view.

I'll click the Method link and scroll down to the es, and show you that there are two versions of the equals method. The equals method is case sensitive. It compares the string to the string of another object. There is also equals ignore case, so you can do a non-case sensitive comparison. So I'll close the Help screen, and I'm going to change my syntax so that instead of using the double equals operator, I'll use the equals method. If (s1.equals(s2)). I'll save and run the application and now I get They Match! Now for non-case sensitive comparisons, use the equals no case method.

I'll go to the second string and change the welcome word to uppercase. I'll run the application and I get They don't match! because the equals method is case- sensitive, but then I'll come down to the equals method and change it to equalsIgnoreCase I'll fix up the code so it's syntactically correct and I'll run the application again, and now I get They match! Finally, I'll show you one more method. I've shown previously that a string contains an array of characters and you can extract that array of characters and then loop through it one character at a time.

I've moved the cursor below the conditional code, I'll declare variable with the data type of char, open bracket, closed bracket—- that's an array of the primitive data type char-- and I'll name it chars and then I'll call the method toCharArray. So it looks like this, s1.toCharArray(); So now I have an array of characters, then I'll loop through the array and I'd put one character at a time. I'll type for and press Ctrl+Space and I'll chose the for-each iteration. For each variable which is going to be data typed as char with the name of c in the char's array, I'll use System.out. println and I'll output the value of c, the character in that position.

I'll run the application and here is the result. Now I'm outputting the string one character at a time, one line at a time. Take a look at the rest of the documentation for the string class. You'll find all sorts of useful methods that allow you to compare, set, extract and otherwise manipulate string values.

Find answers to the most frequently asked questions about Java Essential Training (2011) .

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Q: Can I safely use Java 8 with this tutorial or do I have to be using Java 6 specifically?
A: Yes, you can use Java 8 with this course.
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