通过枚举enum实现单例

enum Singleton implements Serializable {  
      
    INSTANCE;  
      
    private String name;  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  
    @Override  
    public String toString() {  
        return "[" + name + "]";  
    }  
}