1.饿汉式
public class Single{
private static final Single single = new Single();
private Single(){
}
public static Single getInstance(){
return single;
}
}
2.懒汉式
public class Single{
private static final Single single = null；
private Single(){
}
public static Single getInstance(){
if(single == null ){
return new Single();
}
return single;
}
}
3.防止多线程
