由于直接编写一个完整的应用程序的代码（如Android应用或iOS应用）涉及到多个文件、资源、布局以及可能的后端逻辑，这里我将为你提供几种编程语言中的简短示例，展示它们如何用于编写应用程序的不同部分。-优快云博客

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Java (Android 应用)daruijixie.cn
Java 通常用于编写 Android 应用的后端逻辑。

java
public class MainActivity extends AppCompatActivity {

@Override  
protected void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  
    setContentView(R.layout.activity_main);  

    Button button = findViewById(R.id.my_button);  
    button.setOnClickListener(new View.OnClickListener() {  
        @Override  
        public void onClick(View v) {  
            Toast.makeText(MainActivity.this, "Button clicked!", Toast.LENGTH_SHORT).show();  
        }  
    });  
}

}
2. Kotlin (Android 应用)
Kotlin 是 Android 开发的官方推荐语言。

kotlin
class MainActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {  
    super.onCreate(savedInstanceState)  
    setContentView(R.layout.activity_main)  

    val button = findViewById<Button>(R.id.my_button)  
    button.setOnClickListener {  
        Toast.makeText(this, "Button clicked!", Toast.LENGTH_SHORT).show()  
    }  
}

}
3. Swift (iOS 应用)
Swift 用于编写 iOS 应用。

swift
import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {  
    super.viewDidLoad()  
    // Do any additional setup after loading the view.  

    let button = UIButton(type: .system)  
    button.setTitle("Click Me", for: .normal)  
    button.addTarget(self, action: #selector(buttonClicked), for: .touchUpInside)  
    button.translatesAutoresizingMaskIntoConstraints = false  
    view.addSubview(button)  

    NSLayoutConstraint.activate([  
        button.centerXAnchor.constraint(equalTo: view.centerXAnchor),  
        button.centerYAnchor.constraint(equalTo: view.centerYAnchor)  
    ])  
}  

@objc func buttonClicked() {  
    let alert = UIAlertController(title: "Alert", message: "Button clicked!", preferredStyle: .alert)  
    alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))  
    self.present(alert, animated: true, completion: nil)  
}

}
4. Flutter (跨平台应用)
Flutter 使用 Dart 语言编写跨平台应用。

dart
import ‘package:flutter/material.dart’;

void main() {
runApp(MyApp());
}

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: ‘Flutter Demo’,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: ‘Flutter Demo Home Page’),
);
}
}

class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);

final String title;

@override
_MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
void _incrementCounter() {
// This is an example of a stateful widget update.
// In a real app, this might trigger a network fetch, or update a local database.
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this widget and that it needs to be redrawn.
});
}

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
‘You have pushed the button this many times:’,
),
Text(
‘0’, // Here you would normally use a variable to count the presses.
style: Theme.of(context).textTheme.headline4,
),
],
由于直接编写一个完整的应用程序的代码（如Android应用或iOS应用）涉及到多个文件、资源、布局以及可能的后端逻辑，这里我将为你提供几种编程语言中的简短示例，展示它们如何用于编写应用程序的不同部分。

Java (Android 应用)
Java 通常用于编写 Android 应用的后端逻辑。