- Java 双重比较
- java - 比较器与 Apache BeanComparator
- Objective-C 完成 block 导致额外的方法调用?
- database - RESTful URI 是否应该公开数据库主键?
这个问题在这里已经有了答案:
What is an efficient way to implement a singleton pattern in Java? [closed]
(29 个回答)
5年前关闭。
您知道,自从 Java 5 发布以来,在 Java 中编写单例模式的推荐方法是使用枚举。
public enum Singleton {
INSTANCE;
}
public class ApplicationSingleton {
private static enum Singleton {
INSTANCE;
private ResourceBundle bundle;
private Singleton() {
System.out.println("Singleton instance is created: " +
System.currentTimeMillis());
bundle = ResourceBundle.getBundle("application");
}
private ResourceBundle getResourceBundle() {
return bundle;
}
private String getResourceAsString(String name) {
return bundle.getString(name);
}
};
private ApplicationSingleton() {}
public static ResourceBundle getResourceBundle() {
return Singleton.INSTANCE.getResourceBundle();
}
public static String getResourceAsString(String name) {
return Singleton.INSTANCE.getResourceAsString(name);
}
}
ApplicationSingleton.getResourceAsString("application.name")
Singleton.INSTANCE.getResourceAsString("application.name")
public class ApplicationSingleton implements Serializable {
private static enum Singleton {
INSTANCE;
private Registry registry;
private Singleton() {
long currentTime = System.currentTimeMillis();
System.out.println("Singleton instance is created: " +
currentTime);
registry = new Registry(currentTime);
}
private Registry getRegistry() {
return registry;
}
private long getInitializedTime() {
return registry.getInitializedTime();
}
private List<Registry.Data> getData() {
return registry.getData();
}
};
private ApplicationSingleton() {}
public static Registry getRegistry() {
return Singleton.INSTANCE.getRegistry();
}
public static long getInitializedTime() {
return Singleton.INSTANCE.getInitializedTime();
}
public static List<Registry.Data> getData() {
return Singleton.INSTANCE.getData();
}
}
public class Registry {
private List<Data> data = new ArrayList<Data>();
private long initializedTime;
public Registry(long initializedTime) {
this.initializedTime = initializedTime;
data.add(new Data("hello"));
data.add(new Data("world"));
}
public long getInitializedTime() {
return initializedTime;
}
public List<Data> getData() {
return data;
}
public class Data {
private String name;
public Data(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
}
public class ApplicationSingletonTest {
public static void main(String[] args) throws Exception {
String rAddress1 =
ApplicationSingleton.getRegistry().toString();
Constructor<ApplicationSingleton> c =
ApplicationSingleton.class.getDeclaredConstructor();
c.setAccessible(true);
ApplicationSingleton applSingleton1 = c.newInstance();
String rAddress2 = applSingleton1.getRegistry().toString();
ApplicationSingleton applSingleton2 = c.newInstance();
String rAddress3 = applSingleton2.getRegistry().toString();
// serialization
ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
ObjectOutputStream out = new ObjectOutputStream(byteOut);
out.writeObject(applSingleton1);
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(byteOut.toByteArray()));
ApplicationSingleton applSingleton3 = (ApplicationSingleton) in.readObject();
String rAddress4 = applSingleton3.getRegistry().toString();
List<Registry.Data> data = ApplicationSingleton.getData();
List<Registry.Data> data1 = applSingleton1.getData();
List<Registry.Data> data2 = applSingleton2.getData();
List<Registry.Data> data3 = applSingleton3.getData();
System.out.printf("applSingleton1=%s, applSingleton2=%s, applSingleton3=%s\n", applSingleton1, applSingleton2, applSingleton3);
System.out.printf("rAddr1=%s, rAddr2=%s, rAddr3=%s, rAddr4=%s\n", rAddress1, rAddress2, rAddress3, rAddress4);
System.out.printf("dAddr1=%s, dAddr2=%s, dAddr3=%s, dAddr4=%s\n", data, data1, data2, data3);
System.out.printf("time0=%d, time1=%d, time2=%d, time3=%d\n",
ApplicationSingleton.getInitializedTime(),
applSingleton1.getInitializedTime(),
applSingleton2.getInitializedTime(),
applSingleton3.getInitializedTime());
}
}
Singleton instance is created: 1304067070250
applSingleton1=ApplicationSingleton@18a7efd, applSingleton2=ApplicationSingleton@e3b895, applSingleton3=ApplicationSingleton@6b7920
rAddr1=Registry@1e5e2c3, rAddr2=Registry@1e5e2c3, rAddr3=Registry@1e5e2c3, rAddr4=Registry@1e5e2c3
dAddr1=[Registry$Data@1dd46f7, Registry$Data@5e3974], dAddr2=[Registry$Data@1dd46f7, Registry$Data@5e3974], dAddr3=[Registry$Data@1dd46f7, Registry$Data@5e3974], dAddr4=[Registry$Data@1dd46f7, Registry$Data@5e3974]
time0=1304067070250, time1=1304067070250, time2=1304067070250, time3=1304067070250
public class ApplicationSingleton implements Serializable {
private static ApplicationSingleton INSTANCE;
private Registry registry;
private ApplicationSingleton() {
try {
Thread.sleep(10);
} catch (InterruptedException ex) {}
long currentTime = System.currentTimeMillis();
System.out.println("Singleton instance is created: " +
currentTime);
registry = new Registry(currentTime);
}
public static ApplicationSingleton getInstance() {
if (INSTANCE == null) {
return newInstance();
}
return INSTANCE;
}
private synchronized static ApplicationSingleton newInstance() {
if (INSTANCE != null) {
return INSTANCE;
}
ApplicationSingleton instance = new ApplicationSingleton();
INSTANCE = instance;
return INSTANCE;
}
public Registry getRegistry() {
return registry;
}
public long getInitializedTime() {
return registry.getInitializedTime();
}
public List<Registry.Data> getData() {
return registry.getData();
}
}
//now Registry should be Serializable in order serialization to work!!!
public class Registry implements Serializable {
private List<Data> data = new ArrayList<Data>();
private long initializedTime;
public Registry(long initializedTime) {
this.initializedTime = initializedTime;
data.add(new Data("hello"));
data.add(new Data("world"));
}
public long getInitializedTime() {
return initializedTime;
}
public List<Data> getData() {
return data;
}
// now Data should be Serializable in order serialization to work!!!
public class Data implements Serializable {
private String name;
public Data(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
}
public class ApplicationSingletonTest {
public static void main(String[] args) throws Exception {
String rAddress1 =
ApplicationSingleton.getInstance().getRegistry().toString();
Constructor<ApplicationSingleton> c =
ApplicationSingleton.class.getDeclaredConstructor();
c.setAccessible(true);
ApplicationSingleton applSingleton1 = c.newInstance();
String rAddress2 = applSingleton1.getRegistry().toString();
ApplicationSingleton applSingleton2 = c.newInstance();
String rAddress3 = applSingleton2.getRegistry().toString();
// serialization
ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
ObjectOutputStream out = new ObjectOutputStream(byteOut);
out.writeObject(applSingleton1);
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(byteOut.toByteArray()));
ApplicationSingleton applSingleton3 = (ApplicationSingleton) in.readObject();
String rAddress4 = applSingleton3.getRegistry().toString();
List<Registry.Data> data = ApplicationSingleton.getInstance().getData();
List<Registry.Data> data1 = applSingleton1.getData();
List<Registry.Data> data2 = applSingleton2.getData();
List<Registry.Data> data3 = applSingleton3.getData();
System.out.printf("applSingleton1=%s, applSingleton2=%s, applSingleton3=%s\n", applSingleton1, applSingleton2, applSingleton3);
System.out.printf("rAddr1=%s, rAddr2=%s, rAddr3=%s, rAddr4=%s\n", rAddress1, rAddress2, rAddress3, rAddress4);
System.out.printf("dAddr1=%s, dAddr2=%s, dAddr3=%s, dAddr4=%s\n", data, data1, data2, data3);
System.out.printf("time0=%d, time1=%d, time2=%d, time3=%d\n",
ApplicationSingleton.getInstance().getInitializedTime(),
applSingleton1.getInitializedTime(),
applSingleton2.getInitializedTime(),
applSingleton3.getInitializedTime());
}
}
Singleton instance is created: 1304068111203
Singleton instance is created: 1304068111218
Singleton instance is created: 1304068111234
applSingleton1=ApplicationSingleton@16cd7d5, applSingleton2=ApplicationSingleton@15b9e68, applSingleton3=ApplicationSingleton@1fcf0ce
rAddr1=Registry@f72617, rAddr2=Registry@4f1d0d, rAddr3=Registry@1fc4bec, rAddr4=Registry@1174b07
dAddr1=[Registry$Data@1256ea2, Registry$Data@82701e], dAddr2=[Registry$Data@1f934ad, Registry$Data@fd54d6], dAddr3=[Registry$Data@18ee9d6, Registry$Data@19a0c7c], dAddr4=[Registry$Data@a9ae05, Registry$Data@1dff3a2]
time0=1304068111203, time1=1304068111218, time2=1304068111234, time3=1304068111218
最佳答案
我不知道现在枚举是构建单例的 Java 方式。但是如果你打算这样做,你也可以直接使用枚举。我看不出有什么好的理由将单例封装在一堆静态成员方法后面;一旦你这样做了,你也可以开始编写一个带有私有(private)静态成员的静态类。
关于java - 现在更好的 Java 单例模式?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/5822827/
据我所知,根本不为元素呈现 HTML,或添加 display:none,似乎具有完全相同的行为:两者都使元素消失并且不与 HTML 交互。 我正在尝试禁用和隐藏一个复选框。所以HTML的总量很小;我无
我刚刚读了Android Architecture Tutorial: Developing an App with a Background Service (using IPC) .基本上是 让服
我有两个查询具有相同的结果,现在我想知道哪个查询更优化? 在选择中: select t1.*, sum(t2.value) as total_votes from table1 t1 left joi
有人告诉我,对于 I/O 绑定(bind)的应用程序,非阻塞 I/O 会更好。对于 CPU 密集型应用程序,阻塞 I/O 会好得多。我找不到这种说法的原因。试过谷歌,但很少有文章只是触及这个话题而没有
我有一个算法可以在数字列表中寻找好的对。一个好的配对被认为是索引 i 小于 j 且 arr[i] 1: # Finding the mid of the array
我有一个算法可以在数字列表中寻找好的对。一个好的配对被认为是索引 i 小于 j 且 arr[i] 1: # Finding the mid of the array
我从 API 收到一个 json,我需要解析并修改一个属性值。问题是,我收到的 json 数据的嵌套结构不一致,我无法控制它。 这将禁止我指定在特定深度(如 parsedJson.children[0
我有 451 个城市的坐标。现在我想计算每个城市之间的距离,然后根据该距离对一些结果进行排序。现在我有两个选择: 我可以运行一个循环来计算每个可能的城市组合的距离并将它们存储到一个表中,这将产生大约
对于返回相同结果的不同查询,我有两个查询计划我想知道是否有人可以告诉我哪个“更好”,以及为什么。 SELECT * FROM bids order by (select ranking from us
关闭。这个问题需要更多focused .它目前不接受答案。 想改进这个问题吗? 更新问题,使其只关注一个问题 editing this post . 关闭 7 年前。 Improve this qu
我有一个二维数组。我需要尽可能快地对其执行一些操作(函数每秒将被调用十几次,所以让它变得高效会很好)。 现在,假设我想获取元素 A[i][j],简单地使用 A[i][j] 在速度上有什么不同吗和 *(
在声明或使用字符串的代码中,我通常会看到开发人员这样声明它: string randomString = @"C:\Random\RandomFolder\ThisFile.xml"; 代替: str
这个问题在这里已经有了答案: 关闭 10 年前。 Possible Duplicate: Why don't CSS resets use '*' to cover all elements? 我正
如果我有一个包含许多重复项的 python 列表,并且我想遍历每个项目,而不是重复项,最好使用一个集合(如 set(mylist),或者找到另一种方法来创建没有重复的列表?我想只是循环遍历列表并检查重
在阅读常量接口(interface)反模式时,我发现没有实例的最终常量类比常量接口(interface)更好。 请解释一下怎么做? public interface ConstIfc { publ
我正在查看我继承的一些旧代码,我真的不喜欢某些地方的风格。我真的不喜欢它的外观的一件事是: bool func() { bool ret = true; ret &= test1();
关闭。这个问题是opinion-based 。目前不接受答案。 想要改进这个问题吗?更新问题,以便 editing this post 可以用事实和引文来回答它。 . 已关闭 4 年前。 Improv
我经常发现自己试图使用 boost/QT 信号解耦对象。实现这一点的简单方法是针对我要通信的每个具体类型,创建一个新的信号和插槽签名并连接所有相关对象。这导致了访问者模式,理想情况下我想发出一个访问者
我正在 https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html 上阅读有关 lambda 的内容 在方法
public List getInts() { List xs = new ArrayList(); xs.add(1); // return Collections.unmo
我是一名优秀的程序员,十分优秀!