【初心者エンジニアメモ】Javaで出来る事10選

// Javaコードの一部（OpenOfficeの一部機能の抜粋）
public class OpenOfficeWriter {
    public void createDocument(String title, String content) {
        // ドキュメントを作成する処理
    }

    public void saveDocument(String filePath) {
        // ドキュメントを保存する処理
    }

    // その他の機能に関するコード...
}

// Javaコードの一部（Minecraftの一部機能の抜粋）
public class Block {
    private int type;
    private int durability;

    public Block(int type) {
        this.type = type;
        this.durability = calculateDurability();
    }

    private int calculateDurability() {
        // 耐久度の計算処理
        return 100; // 仮の値
    }

    // その他の機能に関するコード...
}

// MainActivity.java - Activityの実装例
package com.example.myfirstapp;

import android.app.Activity;
import android.os.Bundle;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

<!-- activity_main.xml - レイアウトの実装例 -->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

</RelativeLayout>

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DatabaseConnector {
    private static final String DB_URL = "jdbc:mysql://localhost:3306/mydatabase";
    private static final String DB_USER = "username";
    private static final String DB_PASSWORD = "password";

    public static void main(String[] args) {
        try (Connection connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD)) {
            String sql = "SELECT * FROM employees";
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            ResultSet resultSet = preparedStatement.executeQuery();

            while (resultSet.next()) {
                // データベースから取得した情報を処理する
                System.out.println("Employee ID: " + resultSet.getInt("employee_id"));
                System.out.println("Name: " + resultSet.getString("name"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.TextField;

public class LEDControlApp extends MIDlet {
    private Display display;
    private Form mainForm;
    private TextField ledStatus;

    public LEDControlApp() {
        mainForm = new Form("LED Control");
        ledStatus = new TextField("LED Status:", "", 10, TextField.UNEDITABLE);
        mainForm.append(ledStatus);
    }

    protected void startApp() throws MIDletStateChangeException {
        display = Display.getDisplay(this);
        display.setCurrent(mainForm);
        // ここでLEDの制御や処理を行う
        // LEDの状態を表示
        ledStatus.setString("LED is ON");
    }

    protected void pauseApp() {}

    protected void destroyApp(boolean unconditional) throws MIDletStateChangeException {}
}

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the first number: ");
        double num1 = scanner.nextDouble();

        System.out.print("Enter the second number: ");
        double num2 = scanner.nextDouble();

        System.out.print("Enter the operator (+, -, *, /): ");
        char operator = scanner.next().charAt(0);

        double result;

        switch (operator) {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                if (num2 == 0) {
                    System.out.println("Cannot divide by zero.");
                    return;
                }
                result = num1 / num2;
                break;
            default:
                System.out.println("Invalid operator");
                return;
        }

        System.out.println("Result: " + result);
    }
}

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class IoTDeviceStatusFetcher {
    public static void main(String[] args) {
        String deviceURL = "http://example.com/device/status"; // IoTデバイスの状態を取得するAPIエンドポイント

        try {
            URL url = new URL(deviceURL);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuilder content = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                content.append(inputLine);
            }
            in.close();

            System.out.println("IoTデバイスの状態: " + content.toString());
        } catch (Exception e) {
            System.err.println("エラー: " + e.getMessage());
        }
    }
}

import javax.security.auth.login.LoginContext;
import javax.security.auth.login.LoginException;

public class AuthenticationExample {
    public static void main(String[] args) {
        try {
            LoginContext loginContext = new LoginContext("Sample", new SimpleCallbackHandler());
            loginContext.login();
            System.out.println("Authentication successful");
        } catch (LoginException e) {
            System.err.println("Authentication failed: " + e.getMessage());
        }
    }
}

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.nio.charset.StandardCharsets;
import java.security.Key;
import java.security.NoSuchAlgorithmException;

public class EncryptionExample {
    public static void main(String[] args) {
        try {
            // Generate a secret key
            KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
            keyGenerator.init(128);
            SecretKey secretKey = keyGenerator.generateKey();

            // Encrypt the text
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            String plaintext = "This is a secret message";
            byte[] encryptedText = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));
            System.out.println("Encrypted text: " + new String(encryptedText, StandardCharsets.UTF_8));

            // Decrypt the text
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            byte[] decryptedText = cipher.doFinal(encryptedText);
            System.out.println("Decrypted text: " + new String(decryptedText, StandardCharsets.UTF_8));
        } catch (Exception e) {
            System.err.println("Encryption/decryption failed: " + e.getMessage());
        }
    }
}

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;

public class WebAutomationExample {
    public static void main(String[] args) {
        // Set the path to the chromedriver executable
        System.setProperty("webdriver.chrome.driver", "path/to/chromedriver");

        // Initialize the WebDriver
        WebDriver driver = new ChromeDriver();

        // Navigate to a website
        driver.get("https://example.com");

        // Perform automated actions (e.g., filling forms, clicking buttons)

        // Close the browser
        driver.quit();
    }
}

import java.util.Timer;
import java.util.TimerTask;

public class BatchProcessingExample {
    public static void main(String[] args) {
        Timer timer = new Timer();

        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                // Perform batch processing tasks
                System.out.println("Batch processing executed.");
            }
        };

        // Schedule the task to run every 24 hours (86400000 milliseconds)
        timer.schedule(task, 0, 86400000);
    }
}

public class SystemMonitoringExample {
    public static void main(String[] args) {
        // Monitor system performance

        // If performance is below a threshold, send a notification
        sendNotification("System performance is below threshold.");
    }

    private static void sendNotification(String message) {
        // Code to send notification (e.g., email, SMS)
        System.out.println("Notification sent: " + message);
    }
}