什么是单例设计模式，有哪些例子
1.饿汉：如果应用程序总是创建并使用单例实例或在创建和运行时开销不大
class Single {
private Single(){}
private static Single single= new Single();
public static Single getInstance(){
return single;
}
}
2.懒汉：如果开销比较大，希望用到时才创建就要考虑延迟实例化 Singleton的初始化需要某些外部资源(比如网络或存储设备)
class Single {
private Single(){}
private static Single single= null;
public static Single getInstance(){
if ( single == null ) {
synchronized (Single.class) {
if ( single == null ) {
single = new Single();
}
}
}return single;
}
}
3.静态内部类
class Single {
private Single(){}
private static class SingleHandler{
private static Single single = new Single();
}
public static Single getInstance(){
return Single.SingleHandler.single;
}
}
4.枚举
public class Single {
private Single(){}
public enum SingleEnum {
singleHandler;
private Single single;
private SingleEnum () {
single = new Single();
}
public Single getSingle() {
return single;
}
}
public static Single getInstacne() {
return SingleEnum.singleHandler.getSingle();
}
}
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