Java 单例模式实现详解：代码示例与最佳实践

public class Singleton {

private static Singleton instance;

private Singleton() { // 私有构造函数，防止外部实例化 }

public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; }

public void showMessage() { System.out.println('Hello, World!'); } }