Anonymous inner class in java and their syntax

Question

I'm very new to Java and I'm attempting to write an android app and going through the facebook api. I'm looking at this page, specifically, this

    LoginManager.getInstance().registerCallback(callbackManager,
        new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                // App code
            }

            @Override
            public void onCancel() {
                 // App code
            }

            @Override
            public void onError(FacebookException exception) {
                 // App code   
            }
});

This work just fine, I'm just trying to understand how. I'm not understanding the method in a method and more specifically, how would I extract this if I wanted to write it differently?

I tried creating another class

public class FaceBookCallbackLogin implements FacebookCallback<LoginResult> {



@Override
public void onSuccess(LoginResult loginResult) {
    ....
}

@Override
public void onCancel() {

}

and tried to initiate the login from my MainActivity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    callbackManager = CallbackManager.Factory.create();
    setContentView(R.layout.activity_main);
    info = (TextView)findViewById(R.id.info);
    loginButton = (LoginButton)findViewById(R.id.login_button);
    loginButton.setReadPermissions("email");

    loginButton.registerCallback(callbackManager, new FaceBookCallbackLogin());
}

but, this never calls the onSuccess method in FaceBookCallbackLogin, and I can't call it explicitly because I don't have the param LoginResult.

So, how would i write this so I can have the login in a different class? In the original code, where is the param for onSuccess - LoginResult - coming from?

Teddy · Accepted Answer · 2018-01-16 04:10:17Z

1

The way you have changed from anonymous inner class to separate class looks just fine.

However, in first example you have done this:

LoginManager.getInstance().registerCallback

In second example you have done this:

loginButton.registerCallback

Maybe that is the problem..

answered Jan 16, 2018 at 4:10

Teddy

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Comments

martinomburajr · Accepted Answer · 2018-01-16 03:45:12Z

Okay, So the Javadocs say

"Anonymous classes enable you to make your code more concise. They enable you to declare and instantiate a class at the same time. They are like local classes except that they do not have a name. Use them if you need to use a local class only once".

A benefit of the above is it allows you to be precise about your definition for a particular interface implementation without having to go through the hassle of creating new classes for each implementation. Look at the example below.

interface Foo {
    String saySomething(String something);
}

class Bar {

  public static void main(String [] args) {
      //I want this anonymous inner classes implementation to **uppercase** the strings
      Foo sayUppercase = new Foo() {
          @Override
          public String saySomething(String something) {
              return something.toUpperCase();
          }
      };
      sayUppercase.saySomething("Java");
      //output: JAVA

      Foo sayLowerCase = new Foo() {
          //I want this anonymous inner classes implementation to **lowercase** the strings
          @Override
          public String saySomething(String something) {
              return something.toLowerCase();
          }
       };
       sayLowerCase.saySomething("Java");
      //output: java
  }  
}

Notice how I am implementing the same saySomething method differently without having to create two separate classes (class files) for each implementation. I am almost inlining the implementation of the class.

From an Android perspective this is very useful, imagine having to create a separate class for your click listeners. It is still possible, however it is much more simple and readable to create a simple anonymous inner-class for your implementation of your click-listener

mLoginButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //Perform Action
        }
    });

Is much simpler to read and understand than creating a new class that implements View.OnClickListener like below

public class LoginButtonOnClickListener implements View.OnClickListener {

    @Override
    public void onClick(View view) {
        //Perform action
    }
}

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