[design mode] Singleton mode (consider multithreading)

The following program is written by the teacher, more classic, now forget. Save them first.

1 Importjava.util.ArrayList;2 3  Public Final classSingletonobject {4     Private StaticSingletonobject obj;5     PrivateSingletonobject () {}6     //If you declare synchronization on a method, it becomes a bottleneck for system concurrent access7      Public Staticsingletonobject Getinst () {8         if(obj = =NULL){9             synchronized("AA"){Ten                 if(obj = =NULL){ Oneobj =NewSingletonobject (); A                 } -             } -         } the         returnobj; -     } -  -     //1. Declare an object into a class as a class variable, initialize +     //violated the first article. -     //2.1. Declaring an object in a class as a class variable and not initializing +     //initializing in Static A     //always have an initialization code, where to write? If you write to the static code block, then the class is loaded, it is executed, and the direct write Obj2 = .... The same at     //The above scenario violates the first article below -     //2.2. Declaring an object in a class as a class variable and not initializing -     //writes initialization to the method that gets the object -     //obj2 = new Singletonobject (); -     //The above scenario violates the following second article -     //2.2.1. Declaring an object into a class as a class variable and not initializing in     //The decision to NULL in the get method is initialized -     //The above scenario violates the following article III to     //Final scenario: Both the initialization of the object and the initialization statement cannot be put into the Fetch method +     //which scenario in Java belongs to the model system of a class and executes only once, and does not load when the class is loaded, but only when it is loaded, then this scenario is the final scenario -     //Internal class Solutions the      *     Private Static classinner{ $         //adding an object initialization action to an inner classPanax Notoginseng         Private Static FinalSingletonobject Obj2 =NewSingletonobject (); -     } the      +      Public Staticsingletonobject GetInst2 () { A         //both require lazy loading, do not use not create the         //but also to ensure that the creation of the time will not be created multiple times to create a single case +         //It 's best not to make a null decision every time you get it. -         returnInner.obj2; $     } $      -      Public Static voidmain2 (string[] args) { - System.out.println (Singletonobject.getinst ()); the System.out.println (Singletonobject.getinst ()); - System.out.println (Singletonobject.getinst ());Wuyi     } the      -      Public Static voidMain (string[] args) { Wu          -         LongT1 =System.currenttimemillis (); About         LongStart = 90000000000000001L; $         LongEnd = 90000000000000100L; -         LongRefmax = (Long) math.sqrt (end); -Arraylist<long> primes =NewArraylist<long>(); - Out : A          for(Longi = 2;i <= Refmax; i++){ +              for(Longj = 2;j<= math.sqrt (i); J + +){ the                 if(i% j = 0){ -                     ContinueOut ; $                 } the             } the Primes.add (i); the         } theSystem.out.println ("End"); - Out : in          for(Longi = start;i<=end;i++){ the              for(Long prime:primes) { the                 if(i% prime = = 0){ About                     ContinueOut ; the                 } the             } theSystem.out.print (i+ "\ T"); +         } -         Longt2 =System.currenttimemillis (); theSystem.out.println (t2-t1);Bayi          the          the Out : -          for(inti = 101;i <= 200; i++){ -              for(intj = 2;j<= math.sqrt (i); J + +){ the                 if(i% j = 0){ the                     ContinueOut ; the                 } the             } -System.out.print (i+ "\ T"); the         } the     } the }94 /* the A walk here, the time slice expires, the B runs the b Execution is complete, and the Obj object is the b thread new . the at this point, B executes, a runs again, since the time slice expires from here, after resuming the run, also continues from the current line98 execute the following code, and a thread creates an object About at this point B is created once, a is created once, the outside is at least two objects - */

[design mode] Singleton mode (consider multithreading)