简单的java单例代码

写道：面试的时候碰到的，可要背下来哦

public class ClassicSingleton {
private static ClassicSingleton instance = null;

protected ClassicSingleton() {
// Exists only to defeat instantiation.
}
public static ClassicSingleton getInstance() {
if(instance == null) {
instance = new ClassicSingleton();
}
return instance;
}
}