Java 五中简单的创建单例方法

1.线程不安全

public class SingleTest {

        private static SingleTest single = null;

        public static SingleTest  getSingleTest(){

                if(single == null){

                    single = new SingleTest();

                }

                return single;

        }

}

2.同步锁

public class SingleTest {

        private static SingleTest single = null;

        public static synchronized SingleTest  getSingleTest(){

                if(single == null){

                    single = new SingleTest();

                }

                return single;

        }

}

3.减少锁的范围

public class SingleTest {

        private static SingleTest single = null;

        public static SingleTest  getSingleTest(){

                if(single == null){

                  synchronized(this){

                        if(single  == null){

                            single = new SingleTest();

                         }

                    }

                }

                return single;

        }

}

4.静态初始化

public class SingleTest {

        private static SingleTest single = null; 

        static {

            single = new SingleTest();

        }

        public static SingleTest  getSingleTest(){

                return single;

        }

}

5.静态内部类

public class SingleTest {

        private static class SingleHolder {

              private static SingleTest single = new SingleTest ();

        }

        public static SingleTest  getSingleTest(){

            return SingleHolder.single ;

        }

}