//饿汉式 提前生成了单例对象
class Singleton{
private static final Singleton instance=new Singleton(); private Singleton(){} public static Singleton getInstance(){
return instance;
} } //懒汉式 调用的时候才会生成对象
class Singleton11
{
private static Singleton11 instance;
private Singleton11(){} public static Singleton11 getInstance(){
if (instance==null)
{
instance=new Singleton11();
}
return instance;
}
} //多例模式
class Color
{
private static final Color Red=new Color("红色");
private static final Color Green=new Color("绿色");
private static final Color Blue=new Color("蓝色"); private String color;
private Color(String color){
this.color=color;
} public static Color getInstance(String color){
switch (color)
{
case "红色": return Red;
case "绿色": return Green;
case "蓝色": return Blue;
default: return null; }
} public String print(){
return this.color;
}
} public class TestSingleton{
public static void main(String[] args){
Singleton A=Singleton.getInstance();
Singleton B=Singleton.getInstance();
System.out.println(A==B); Singleton11 A11=Singleton11.getInstance();
Singleton11 B11=Singleton11.getInstance();
System.out.println(A11==B11); Color red=Color.getInstance("红色");
Color green=Color.getInstance("绿色");
Color blue=Color.getInstance("蓝色"); System.out.println(red.print());
System.out.println(green.print());
System.out.println(blue.print());
}
}
多线程的情况:
class Singleton{
private static volatile Singleton instance=null; //直接操作主内存 比操作副本效果好
private Singleton(){
System.out.println(Thread.currentThread().getName()+"******实例化Singleton******");
}
public static Singleton getInstance(){
if (instance==null){
synchronized (Singleton.class){ //此处同步的是new Singleton() 提升多线程效率
if (instance==null){ //此处的判断 对应上面的if (instance==null) 多个线程进来
instance=new Singleton();
}
}
}
return instance;
}
public void print(){
System.out.println("wwww.mldn.com");
}
}
public class SingleInstance {
public static void main(String[] args) {
// Singleton s=Singleton.getInstance();
// s.print();
// Singleton ss=Singleton.getInstance();
// ss.print();
// System.out.println(s==ss);
for (int i=0;i<3;i++){
new Thread(()-> System.out.println(Singleton.getInstance()),"单例"+i).start();
}
}
}