State mode of design mode

State mode of design mode

State mode, also known as the state object pattern (pattern of Objects for States), state mode is the behavior pattern of the object. State mode allows an object to change its behavior when its internal state changes. This object looks like it has changed its class.

Example: A person laughs when he is happy (laughs), cries (Tears of joy), and laughs when he is unhappy (a wry smile) and cries (weeping). First edition: Complete the function in the simplest way

 Public classPerson {PrivatePersonstate State;  PublicPerson (personstate state) { This. State =State ; }         Public voidchangestate (personstate state) { This. State =State ; }         Public voidSmile () {if(state = =personstate.happy) {System.out.println (Laugh); } Else if(state = =personstate.unhappy) {System.out.println (Wry smile); }    }         Public voidcry () {if(state = =personstate.happy) {System.out.println ("The joy of weeping."); } Else if(state = =personstate.unhappy) {System.out.println ("Crying and weeping."); }    }    }enumpersonstate {HAPPY, unhappy}

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Test

 Public Static void Main (string[] args) {    new person (personstate.happy);    P.smile ();    P.cry ();    P.changestate (personstate.unhappy);    P.smile ();    P.cry ();}

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OK, the problem is solved, the person can laugh and cry in Happy and unhappy to show a different state, the problem comes, one is not only happy and unhappy two states, such as normal people will also laugh (smile) will Cry (tears), at this time to respond to this state, You can only modify the code of the person class!

Version two: decoupling

Abstract the state of a person

 Public Interface personstate {    void  smile ();     void cry ();}

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Cry and laugh when you are happy

 Public class Implements personstate {    @Override    publicvoid  smile () {        System.out.println (" Laughter ");    }    @Override    publicvoid  Cry () {        System.out.println ("Joy and Cry");}    } 

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Cry and laugh when you are not happy

 Public class Implements personstate {    @Override    publicvoid  smile () {        System.out.println (" Wry Smile ");    }    @Override    publicvoid  Cry () {        System.out.println ("weep bitterly");}    } 

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Person

 Public classPerson {PrivatePersonstate State;  PublicPerson (personstate state) { This. State =State ; }         Public voidchangestate (personstate state) { This. State =State ; }         Public voidSmile () {state.smile (); }         Public voidcry () {state.cry (); }}

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Test

 Public class Test {    publicstaticvoid  main (string[] args) {        new personhappystate ();         New Person (happy);        P.smile ();        P.cry ();         New personunhappystate ();        P.changestate (unhappy);        P.smile ();        P.cry ();    }}

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OK, then add normal state when crying, laugh is very simple, just implement Personstate interface, realize their own smile and cry method.

State mode of design mode