xxii Introduction
final EditText et = findViewById(R.id.edit);
final Button btn = findViewById(R.id.btn);
final TextView text = findViewById(R.id.text);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String entered = et.getText().toString();
text.setText("You entered '" + entered +
"' and pressed 'Go'");
}
});
}
}
Here are a few notes about the previous Java code:
The public in front of the class says that it is visible from everywhere.
It cannot be omitted here since otherwise the framework could not use
the class.
The setContentView() changes something by virtue of the “set,”
which is such a common construct that you might want to write it
more concisely as contentView = s.th.instead, even with a variable
of name "contentView" not actually existing or being private. A couple
of competitor languages allow for this type of syntax. In Groovy for
example, you can write contentView = s.th.and the language will
internally translate it to setContentView().
The final in front of the three declarations is necessary in Java up to
version 7 because the variables are going to be used in the anonymous
inner class that comes a little later.
Also, for the setOnClickListener() method, you might want to use
.onClickListener = s.th. instead. It’s the same for the .setText() a
little later.
The argument to setOnClick-Listener() is an object of an anonymous
inner class; it is already an abbreviation of first declaring and then
instantiating and using it. But you could be even more expressive with
syntax like btn -> do s.th. or similar, just not in the Java language
(well, at least not before Java 8).
For the et.getText() method, you could just as well write something
like et.text, which would express the same thing but is shorter.
A sister project that does the same thing but with Kotlin support is written in the Kotlin
language as follows:
package de.pspaeth.simplekotlin
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
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