1. Android (Java/Kotlin)e-energy.cn
   Java 示例 (Android Studio):

java
public class MainActivity extends AppCompatActivity {

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

    // ... 其他代码  
}  

}
Kotlin 示例 (Android Studio):

kotlin
class MainActivity : AppCompatActivity() {

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

    // ... 其他代码  
}  

}
2. iOS (Swift/Objective-C)
Swift 示例 (Xcode):

swift
import UIKit

class ViewController: UIViewController {

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

}
Objective-C 示例 (Xcode):

objc
#import “ViewController.h”

@interface ViewController ()

@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  }

@end
3. Web (React/Vue/Angular)
React 示例 (Create React App):

jsx
import React from ‘react’;
import ReactDOM from ‘react-dom’;

function App() {
return (

);
}

ReactDOM.render(, document.getElementById(‘root’));
Vue 示例 (Vue CLI):

vue

Angular 示例 (Angular CLI):

typescript
import { Component } from ‘@angular/core’;

@Component({
selector: ‘app-root’,
templateUrl: ‘./app.component.html’,
styleUrls: [‘./app.component.css’]
})
export class AppComponent {
title = ‘My App’;
}
(在 app.component.html 中你会有

{{ title }}

来显示 “My App”)

4. 后端 (Node.js/Python/Ruby)
   Node.js (Express) 示例:

javascript
const express = require(‘express’);
const app = express();
const port = 3000;

app.get(‘/’, (req, res) => {
res.send(‘Hello, World!’);
});

app.listen(port, () => {
console.log(App listening at http://localhost:${port});
});
Python (Flask) 示例:

python
from flask import Flask, render_template
app = Flask(name)

@app.route(‘/’)
def hello_world():
return ‘Hello, World!’

if name == ‘main’:
app.run(debug=True)
Ruby (Ruby on Rails) 示例 (需要先创建一个Rails项目):

在 app/controllers/application_controller.rb 或其他控制器中:

ruby
class ApplicationController < ActionController::Base

… 其他代码

def hello
render plain: “Hello, World!”
end
end
然后在路由文件中添加对应的路由。

请注意，这些只是最基础的示例，实际的App开发会涉及更多的复杂性和特性。由于生成一个完整的App代码涉及多个方面（如前端、后端、数据库、界面设计等），并且不同的App平台（如Android、iOS、Web）需要使用不同的开发工具和语言，所以在这里我会给出每种语言或框架的简要示例和说明，而不是完整的App代码。

1. Android (Java/Kotlin)
   Java 示例 (Android Studio):

java
public class MainActivity extends AppCompatActivity {

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

    // ... 其他代码  
}  

}
Kotlin 示例 (Android Studio):

kotlin
class MainActivity : AppCompatActivity() {

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

    // ... 其他代码  
}  

}
2. iOS (Swift/Objective-C)
Swift 示例 (Xcode):

swift
import UIKit

class ViewController: UIViewController {

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

}
Objective-C 示例 (Xcode):

objc
#import “ViewController.h”

@interface ViewController ()

@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  }

@end
3. Web (React/Vue/Angular)
React 示例 (Create React App):

jsx
import React from ‘react’;
import ReactDOM from ‘react-dom’;

function App() {
return (

);
}

ReactDOM.render(, document.getElementById(‘root’));
Vue 示例 (Vue CLI):

vue

Angular 示例 (Angular CLI):

typescript
import { Component } from ‘@angular/core’;

@Component({
selector: ‘app-root’,
templateUrl: ‘./app.component.html’,
styleUrls: [‘./app.component.css’]
})
export class AppComponent {
title = ‘My App’;
}
(在 app.component.html 中你会有

{{ title }}

来显示 “My App”)

4. 后端 (Node.js/Python/Ruby)
   Node.js (Express) 示例:

javascript
const express = require(‘express’);
const app = express();
const port = 3000;

app.get(‘/’, (req, res) => {
res.send(‘Hello, World!’);
});

app.listen(port, () => {
console.log(App listening at http://localhost:${port});
});
Python (Flask) 示例:

python
from flask import Flask, render_template
app = Flask(name)

@app.route(‘/’)
def hello_world():
return ‘Hello, World!’

if name == ‘main’:
app.run(debug=True)
Ruby (Ruby on Rails) 示例 (需要先创建一个Rails项目):

在 app/controllers/application_controller.rb 或其他控制器中:

ruby
class ApplicationController < ActionController::Base

… 其他代码

def hello
render plain: “Hello, World!”
end
end
然后在路由文件中添加对应的路由。

请注意，这些只是最基础的示例，实际的App开发会涉及更多的复杂性和特性。