單例模式--延時初始化

單例模式特點：構造函數聲明為private，對象獲取通過函數調用。

基本單例模式（餓漢模式）：

final class Singleton{
    private static Singleton s=new Singleton(47);
    private int i;
    private Singleton(int x){i=x;}

    public static Singleton getReference(){
        return s;
    }
    public int getValue(){return i;}
    public void setValue(int x){i=x;}
}

靜態延時初始化（懶漢模式）：

final class StaticSingleton{
    private static StaticSingleton s;
    private int i;
    private StaticSingleton(int x){i=x;}

    public static StaticSingleton getReference(){
        if(s == null){
            s=new StaticSingleton(47);
        }
        return s;
    }

    public int getValue(){return i;}
    public void setValue(int x){i=x;}
}
類加載延時初始化：

final class InnerSingleton{
    private static InnerSingleton s;
    private int i;
    private InnerSingleton(int x){i=x;}

    private static class SingletonHolder{
        static InnerSingleton instance =new InnerSingleton(47);
    }
    public static InnerSingleton getReference(){
        return SingletonHolder.instance;
    }

    public int getValue(){return i;}
    public void setValue(int x){i=x;}
}
查找注冊方式：
接口：

public interface EmployeeManagement {
    static String name="";
    public void setName(String name);
}
單例模式類：

final class Employee implements EmployeeManagement{
    static String name;
    private static Map<String,Employee> map = new HashMap<String,Employee>();
    static{
        Employee single = new Employee();
        map.put(single.getClass().getName(), single);
    }
    public void setName(String name){
        this.name=name;
    }
    protected Employee(){}
    protected Employee(String name){this.setName(name);}
    public static Employee getInstance(String name) {
        if(name == null) {
            name = Employee.class.getName();
            System.out.println("name == null"+"--->name="+name);
        }
        if(map.get(name) == null) {
            if(map.get(name) == null) {
                try {
                    map.put(name, (Employee) Class.forName(name).newInstance());
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
        return map.get(name);
    }

    public void getInfo(){
        System.out.println(name+" is here .");
    }
}
應用實例：

public class RegistryService {

    public static void main(String[] args) {
        Employee em=Employee.getInstance("singleton.Employee");
        em.setName("SuYU");
        em.getInfo();
    }
}

資源：
https://share.weiyun.com/5kLvDQS
https://share.weiyun.com/5LRwSxS