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Overloading method names with different signatures

From: Java Essential Training

Video: Overloading method names with different signatures

The Java programming language allows you to create methods that share the same name, but have different signatures. A method signature is the unique combination of keywords and arguments that the method receives. For example, the standard main method receives an argument which is an array of strings. You can create your own custom methods in your class and where necessary, you can create multiple methods that share the same name as long as they have different signatures. The Java Virtual Machine determines at runtime which version of a method it should run, depending on what arguments are passed to it.

Overloading method names with different signatures

The Java programming language allows you to create methods that share the same name, but have different signatures. A method signature is the unique combination of keywords and arguments that the method receives. For example, the standard main method receives an argument which is an array of strings. You can create your own custom methods in your class and where necessary, you can create multiple methods that share the same name as long as they have different signatures. The Java Virtual Machine determines at runtime which version of a method it should run, depending on what arguments are passed to it.

Let's create a few very simple methods. I'm working in a beginning main class in the project MethodOverloading. I'll place the cursor after the static void main method and I'll create a new method using private static, I'll set the methods return value to int and I'll name the method addValues. For this first version of the method I'll receive two arguments, and they'll both be data typed as integers. I'll name the first one int1, and the second one int2.

The body of the method will add up these two values and return the result. I'll do it on a single statement. return int1 + int2. In the main method I'll declare two starting variables; I'll declare them both as integers. I'll name the first one value1 and I'll set it to a value of 5. And I'll create the second one as value2 and set it to a value of 10. I'll declare an integer result variable and get its value from addValues and I'll pass in value1 and value2 and I'll output the result using System.out.println, (The result is" and then + result) I'll Save and Run the application and everything is fine. The result is 15.

Now I'm going to add two more versions of this method, I'll copy the existing version and I'll paste it in, making sure I do this inside the body of the class and notice right now that I'm getting warnings that I have duplicate methods. The reason they are duplicate is not just because of the name, but also because they receive the same number and data types of arguments. So unlike other languages like JavaScript or ActionScript, I don't need to rename the second version of the method. I can just change the method signature. I have this method receive a third argument.

The data type again will be int and the name will be int3, and I'll change the return statement to add that variable as well. As soon as I make the change, all the errors go away. I'm still left with a warning that I have a method that's not currently being called. But I'll fix that. I'll go back to my main method and create a third value and I'll set it to 15 and then I'll change the way I'm calling the method and I'll pass in value3. I'll Save the change and Run the application and now I get the result as 30. Clearly I'm now running the second version of the method, so you can have more than one method of the same name as long as they have different numbers of arguments.

But you can also distinguish methods from each other by the data types of the arguments. I'll create one more version of the add values method. My code is getting a little longer now, so I'll maximize my editor and move the cursor under all the other methods and I'll create another private, static and returns an int, and once again it will have the name addValues. This version of the method will have two arguments but they'll both be strings, and I'll call them val1 and val2. Now in order to add these values together I need to convert them to integers, so within the method I'll declare two integer variables.

The first one will be called value1 and I'll set its value using integer.parseInt, and I'll pass in val1, and then I'll make a copy of that line, I'll change the second version to create a variable called value2, and it will get its value from val2, and then I'll do a return statement and I'll add together value1 and value2. So now I have three versions of the method, addValues with 2 integers, addValues with 3 integers and addValues with two strings.

I'll go back up to the code and I'll create a couple of new variables, the first one will be a string and it will be named string1, and I'll give it a value of 10, but because it's a string it has to wrapped in double quotes. I'll set string2 to a value of 25, then I'll create a variable called result2, and I'll get its values from the addValues method. And notice when I press Ctrl+Space Eclipse shows me all the different versions of the method that are available. The version with the two integers, the version with two strings and the version with the three ints, I'll choose the version with the two strings.

and I'll pass in string1 and string2. I'll make a copy of my println command and paste it down here, and I'll output the value of result2. I'll run the application and the second version is clearly calling the version that receives the strings. So this sort of coding is called method overloading. When you overload a method, you are reusing the same method name, but you're creating alternative signatures. This is a good coding strategy in Java to handle situations where in one circumstance you have a certain set of variables, in another circumstance you got another set and where the data types can differ as well.

By simply reusing the method names, but having distinct method signatures, it makes your coding much more flexible. And again, this is something that Java does that other languages in the C family might not. JavaScript and ActionScript for example, don't allow method overloading. In those languages each method name can only be used once, they have other strategies such as the ability to receive variable numbers of parameters in a method, but this capability of Java can be valuable to your application design.

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This video is part of

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Java Essential Training

71 video lessons · 71798 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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