Java Learning Note (24): Single case design mode singleton

Why use singleton design mode?

Suppose a tool class (tools) with an array of operations is designed, there is a hammer method (Hammer), and if you do not use the singleton design pattern, each time you want to invoke the Hammer method, you need a new tools class.

1 classtools{2     //Hammer3      Public voidHammer () {4SYSTEM.OUT.PRINTLN ("Use the Hammer");5     }6 }7  8  Public classToolsdemo {9      Public Static voidMain (string[] args) {Ten     //need to use a hammer One     NewTools (). Hammer (); A     //need to use a hammer -     NewTools (). Hammer (); -     //need to use a hammer the     NewTools (). Hammer (); -     } -}

Run results

Using a hammer with a hammer use a hammer

This is a waste of memory resources, like a class of people eat walnuts need to hit with a hammer, there is no need for each student to buy a hammer, just buy a hammer, who want to eat walnuts who go with a hammer, greatly saving the cost.

So it leads to the singleton single-case design mode, only need to generate in memory once, later want to use just call this memory, there is no need to re-in the heap every time new tools class

1 classtools{2     //(1): You must first create a static object in this class3     Private StaticTools instance =NewTools ();4     //(2): privatization of its own constructor to prevent the outside world from creating new objects through the constructor5     PrivateTools () {}6     //(3): Additional exposure to a public static method used to obtain its own object7      Public StaticTools getinstance () {8         returninstance;9     }Ten  One     //Hammer A      Public voidHammer () { -SYSTEM.OUT.PRINTLN ("Use the Hammer"); -     } the } -  -  Public classToolsdemo { -      Public Static voidMain (string[] args) { +         //need to use a hammer - tools.getinstance (). Hammer (); +         //need to use a hammer A tools.getinstance (). Hammer (); at         //need to use a hammer - tools.getinstance (). Hammer (); -     } -}

Run results

Using a hammer with a hammer use a hammer

Java Learning Note (24): Single case design mode singleton