单例模式(逐步递进的三种)
package 单例模式A;public class SingletonPatternA {@SuppressWarnings({ "static-access", "unused" })public static void main(String args[]){ Emperor emperor1 = Emperor.getInstance(); emperor1.emperorInfo(); Emperor emperor2 = Emperor.getInstance(); emperor1.emperorInfo(); if(emperor1 == emperor2){ //判断emperor1 和emperor2 是否是同一个人 System.out.println(emperor1+"=="+emperor2+" true."); }}}class Emperor {private static Emperor emperor = null;public Emperor(){}public static Emperor getInstance(){if(emperor ==null){emperor = new Emperor();}return emperor;}public static void emperorInfo(){System.out.println("我是皇帝某某···");}}//**************************************************************************package 单例模式A;public class SingletonPatternB { @SuppressWarnings("static-access")public static void main(String args[]){ new Emperor2().getInstance().emperorInfo(); }}class Emperor2 {private static Emperor2 emperor2=null; Emperor2(){}@SuppressWarnings("static-access")public Emperor2 getInstance(){if(this.emperor2 == null) //只有这儿和第一种不同this.emperor2 = new Emperor2();return this.emperor2;}public static void emperorInfo(){System.out.println("我是皇帝某某···");}}//***********************************************************************package 单例模式A;public class SingletonPatternC {@SuppressWarnings("static-access")public static void main(String args[]){Emperor3 emperor3 = Emperor3.getInstance();emperor3.emperorInfo();Emperor3 emperor33 = Emperor3.getInstance();emperor33.emperorInfo();if(emperor3 == emperor33){System.out.print("他们是同一个对象！");}}}class Emperor3 {private static final Emperor3 emperor3 = new Emperor3(); //变化private Emperor3(){}public synchronized static Emperor3 getInstance(){ //防止并发 多线程问题return emperor3;}public static void emperorInfo(){System.out.println("我是皇帝某某···");}}//当然了，我们是推荐第三种的！！！！！！！！！！！！！！！！！！！！！！！！！！！！！