How to Use Basic Generics Syntax in Java

See Java: Tips and Tricks for similar articles.

You can create a class in Java that defines one or more placeholders for data type. The placeholders are known as generics because the class is not determined until compile time. Generics are notated by angle brackets (< and >). For example, we might wish to create a class that contains a method that accepts an argument of any data type and displays the value of the argument. Because we don't know the data type when we are developing the class, we must use a generic for the method argument data type. To apply basic generics syntax in Java, follow these four steps.

  1. Open your text editor and type in the following Java statements:Java Source for Basic GenericsThe class that contains the generic syntax is named GenericsDisplay. Note the generic parameter T after the class name on line 10. We could use any other letter or a longer name if we wished, but using the one-letter parameter name "T" (as in "Type") is considered best practice, as this letter is used in the Core API. Notice that the data type of the argument in the display method is T. At compile time, the generic argument type will be replaced with the data type of the parameter that is passed to the method. In the output of this method the value of the argument is displayed along with its data type. In this way, we can verify at run time that the correct data type was communicated to the class using the generic parameter. Two objects are instantiated in the main method, each using a different class name as the value for the generic parameter. Now, all occurrences of T in the GenericsDisplay class with be replaced with the class provided when the object is instantiated (e.g., String). The main method calls the display method for each object.
  2. Save your file as BasicGenericsSyntax.java.
  3. Open a command prompt and navigate to the directory containing your Java program. Then type in the command to compile the source and hit Enter.Compile Source for Basic Generics
  4. Type in the command to run your program and hit Enter. Notice in the output that a String variable and a Date variable were each successfully passed to the generic class method.Run for Basic Generics

Related Articles

  1. How to Check Object Type in Java
  2. How to Create a Jar File in Java
  3. How to Compile Packages in Java
  4. How to Throw an Exception in Java
  5. How to Create an Exception Class in Java
  6. How to Use the super Keyword to Call a Base Class Constructor in Java
  7. How to Use the Comparator.comparing Method in Java 8
  8. How to Use System.in in Java
  9. How to Call an Interface Method in Java
  10. How to Add a Time Zone in the Java 8 Date/Time API
  11. How to Rethrow an Exception in Java
  12. How to Use the instanceof Operator with a Generic Class in Java
  13. How to Instantiate an Object in Java
  14. How to Filter Distinct Elements from a Collection in Java 8
  15. How to Create a Derived Class in Java
  16. How to Skip Elements with the Skip Method in Java 8
  17. How to Create a Java Bean
  18. How to Implement an Interface in Java
  19. How to Compare Two Objects with the equals Method in Java
  20. How to Set PATH from JAVA_HOME
  21. How to Prevent Race Conditions in Java 8
  22. How to Write a Block of Code in Java
  23. How to Display the Contents of a Directory in Java
  24. How to Group and Partition Collectors in Java 8
  25. How to Create a Reference to an Object in Java
  26. How to Reduce the Size of the Stream with the Limit Method in Java 8
  27. How to Write an Arithmetic Expression in Java
  28. How to Format Date and Time in the Java 8 Date/Time API
  29. How to Use Comparable and Comparator in Java
  30. How to Break a Loop in Java
  31. How to Use the this Keyword to Call Another Constructor in Java
  32. How to Write a Unit Test in Java
  33. How to Declare Variables in Java
  34. How to Override Base Class Methods with Derived Class Methods in Java
  35. How to Use Serialized Objects in Java
  36. How to Write Comments in Java
  37. How to Implement Functional Interfaces in Java 8
  38. How to Write Type Parameters with Multiple Bounds in Java
  39. How to Add Type and Repeating Annotations to Code in Java 8
  40. How to Use Basic Generics Syntax in Java (this article)
  41. How to Map Elements Using the Map Method in Java 8
  42. How to Work with Properties in Java
  43. How to Write while and do while Loops in Java
  44. How to Use the finally Block in Java
  45. How to Write for-each Loops in Java
  46. How to Create a Method in Java
  47. How to Continue a Loop in Java
  48. How to Handle Java Files with Streams
  49. How to Create an Interface Definition in Java
  50. How Default Base Class Constructors Are Used with Inheritance