Java单例模式

来源：http://www.cnblogs.com/whgw/archive/2011/10/05/2199535.html

 

Java中单利模式有三种： 懒汉式、饿汉式、登记试

饿汉式：

public class Singleton {
    private Singleton() {}

    private static Singleton instance = new Singleton();

    public static Singleton getInstance() {
        return instance;
    }
}

懒汉式：

public class Singleton {
    private Singleton() {}

    private static Singleton instance = null;

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

登记式：

import java.util.HashMap;
import java.util.Map;

public class Singleton {
    private static Map<String, Singleton> map = new HashMap<String, Singleton>();

    static {
        Singleton single = new Singleton();
        map.put(single.getClass().getName(), single);
    }

    protected Singleton() {}

    public static Singleton getInstance(String name) {
        if(name == null) {
            name = Singleton.class.getName();
        }

        if(map.get(name) == null) {
            try {
                map.put(name, (Singleton)Class.forName(name).newInstance());
            } catch(Exception e) {
                e.printStackTrace();
            }
        }
        return map.get(name);
    }
}