Java: Accessing Constructors, Methods, & Fields Using Reflection

IN THIS COURSE

• 1.  Course Overview
  2m 57s
  In this video, you’ll learn more about your instructor and this course. In this course, you’ll learn how to extract information and metadata about the constructors in a class. You’ll see how the .getConstructors method only returns public constructors. You’ll learn that to access the private or protected constructors, you’ll need the .getDeclaredConstructors method. Then, you’ll explore metadata about fields using Reflection. FREE ACCESS
• 2.  Accessing Constructors Using Reflection
  9m 33s
  Here, you’ll watch a demo. In this demo, you’ll learn to instantiate objects of a given class. First, you’ll examine the Java docs for the class you see mentioned onscreen. These refer to using the reflection API's in order to construct new instances of a class. You’ll see a blank Main.java and an Employee.java file as well. FREE ACCESS
• 3.  Creating Objects Using Constructor Handles
  8m 54s
  Here, you’ll watch a demo. You’ll pick up where you left off at the end of the last demo. There, you used the newInstance method on a constructor object. You used that to create an object of a specific class. That code is onscreen now. It's the employeeClass you’ll be instantiating in this manner. This time it's the noArgumentConstructor you’ll use. FREE ACCESS
• 4.  Accessing Field Metadata
  10m 14s
  Here, you’ll watch a demo. You’ll learn more about fields. In the context of a reflection, the term field is used for member variables. Member variables whether private, public, or protected, static or non-static, are all covered by the reflection API for fields. This does not include methods. Those are covered by a different API. FREE ACCESS
• 5.  Getting and Setting Field Values
  8m 52s
  Here, you’ll watch a demo. Here, you’ll clear up the current contents of your main method and then add in a new import statement that you’ll need. This is java.lang.reflect.Modifier. It allows you to interpret the modifiers applied to a field or a member function. Onscreen you’ll see the code you’ll need for fields in your employeeClass. You’ll use the class.forName method. It takes in a string and returns the class object. FREE ACCESS
• 6.  Accessing and Updating Private and Protected Fields
  9m 13s
  Here, you’ll watch a demo. Here, you’ll run the code and examine the output you see onscreen. You can see from the output that initially, your employee object has no real values for any of its fields. Initially, the only field which is populated is the ID. But the Name and Title are both unknown, the salary is 0, and the Department and list of Committees are both set to null. FREE ACCESS
• 7.  Accessing Public, Private, and Protected Methods
  8m 36s
  Here, you’ll watch a demo. You’ll work with methods, which are member functions. You’ll begin by importing a specific class. This is a java.lang.reflect.Method. This class contains much of the functionality in the Java Reflection APIs that's relevant to working with methods. You’ll note a method can include an abstract method as well. Onscreen, you’ll see the URL which hosts the Java Docs for java.lang.reflect.Method. FREE ACCESS
• 8.  Viewing Method Parameters, Annotations, and More
  7m 14s
  Here, you’ll watch a demo. You’ll turn your attention to a user-defined class, specifically the employee class, which you now see onscreen. This particular iteration of the employee class is slightly different than in previous demos. That's because your focus is on many different types of methods rather than fields or constructors. You’ll see a few fields on lines 10 through 15, and then on line 17, you have a constructor that's private. FREE ACCESS
• 9.  Accessing Annotations on Methods
  7m 8s
  Here, you’ll watch a demo. In this demo, you’ll learn how reflection and annotations interact. You’ll begin by importing additional bits of functionality. Onscreen you’ll see you’ve imported java.lang.reflect.Modifier,and. You’ll then add the required code. You’ll factor out a code into a separate method called printMethodProperties. This is defined onscreen starting on line 9. printMethodProperties takes in one input argument which is of type method. FREE ACCESS
• 10.  Recognizing Annotation Runtime Policy Implications
  8m 12s
  Here, you’ll watch a demo. In this demo, you’ll recognize annotation runtime policy implications. You’ll learn the printMethodProperties utility can be very helpful. It provides you with information about any method that you pass in. You’ll invoke it one more time now. You first need to get a method object. You’ll do this on line 47 by invoking employeeClass.getMethod. You’ll pass in the name of the method you’re looking for. FREE ACCESS
• 11.  Identifying Getters and Setters Using Heuristics
  10m 14s
  Here, you’ll watch a demo. In this demo, you’ll move on to another aspect of using reflection to invoke methods on a specific object. This is a logical next step and it's an important operation in real-world uses of reflection. Onscreen, you’ll see a method called isGetter defined. This is a private static method. It returns a boolean value. It takes in a method object. FREE ACCESS
• 12.  Invoking Functions Using Reflection
  4m 32s
  Here, you’ll watch a demo. In this demo, you’ll move on to changing the state of an object by invoking the setter methods on that object. First, you’ll add in some additional code. Onscreen, you’ll see you have yet another for loop. This one starts on line 83. This for loop also iterates over all of the declared methods in our employeeClass. This for loop has a loop variable called method with the lowercase m. FREE ACCESS
• 13.  Course Summary
  2m 33s
  In this video, you’ll summarize what you’ve learned in this course. You’ve learned how to extract information and metadata about the constructors in a class. You saw how the .get constructors method only returns the public constructors in a class. You used Reflection to obtain handles to individual constructors in a class. You created new objects of the class using those handles via the .new instance method. FREE ACCESS