java的三大特性，封裝，繼承，多態

封裝?

/**?
?*?所謂封裝，就是將對象具有的成員變量和成員函數包裝和隱藏起來，讓外界無法直接使用，?
?*?被封裝的成員只能通過某些特定的方式才能訪問。??
?*?實現封裝有兩個步驟：?
?*???1、將不能暴露的成員隱藏起來，我們就不能讓其在類的外部被直接訪問或賦值。?
?*??????實現方法是將該成員定義為私有的，在成員定義前加上private訪問權限修飾符。?
?*???2、用公共方法來暴露對該隱藏成員的訪問，可以給成員加上public修飾符，將該成員定義為公共的?
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Package???
?*?@package?:?com.study.feature??
?*?@Description?：封裝性的測試????
?*?@author：lgf????
?*?@date?：2012?三月?12??10:20:35???????????
?*?@version?:?1.0?
?*/??
public?class?Package?{??
????//?使用private隱藏??
????private?String?strValue;??
??
????//?通過get和set進行訪問??
????public?String?getStrValue()?{??
????????return?this.strValue;??
????}??
????public?void?setStrValue(String?strValue)?{??
????????this.strValue?=?strValue;??
????}??
}??

繼承?
父類 ExtendsFather.java?

/**?
?*?繼承是一種聯結類的層次模型，并且允許和鼓勵類的重用，它提供了一種明確表述共性的方法。?
?*?對象的一個新類可以從現有的類中派生。?
?*?1.?為什么要使用繼承？?
?*??a.提高程序的擴展性。?
????b.提高了代碼的重用性。?
?????
???2.?子類能繼承到父類的那些方法和屬性?
????第一種：所有的屬性和方法都被子類繼承到了。?
????第二種：?
????a、子類和父類在同一個包下：?
????公有的受保護的屬性和方法被子類繼承到了。?
????b、子類和父類不在同一個包下：?
????公有的方法和屬性被子類繼承到了。?
?????
???3.?子類的對象能調用父類的那些方法和屬性？?
????a、子類和父類在同一個包下：?
????公有的受保護的屬性和方法能被子類調用。?
????b、子類和父類不在同一個包下：?
????公有的方法和屬性能被子類調用。?
????在類和抽象類中，默認的就是受保護的。?
????在接口中，默認的就是公有的。?
?*/??
package?com.study.feature;??
??
/**????
?*?父類?
?*?@className?：ExtendsFather???
?*?@package?:?com.study.feature??
?*?@Description?：繼承測試????
?*?@author：lgf????
?*?@date?：2012?三月?12??10:33:02???????????
?*?@version?:?1.0?
?*/??
public?class?ExtendsFather?{??
????//?定義不同四種修飾符的屬性??
????private?????String?privateValue;??
????protected???String?protectedValue;??
????????????????String?defaultValue;??
????public??????String?publicValue;??
??????
????//?定義不同四種修飾符的方法??
????private?void?privateFunction(){??
????????System.out.println("privateFunction");??
????}??
??????
????protected?void?protectedFunction(){??
????????System.out.println("protectedFunction");??
????}??
??????
????void?defaultFunction(){??
????????System.out.println("defaultFunction");??
????}??
??????
????public?void?publicFunction(){??
????????System.out.println("publicFunction");??
????}??
}??

同包下的子類 ExtendsChildrenSamePackage.java?

package?com.study.feature;??
/**?
*??
*??
*?@className?：ExtendsChildrenSamePackage???
*?@package?:?com.study.feature??
*?@Description?：?同一個包下面的繼承關系????
*?@author：lgf????
*?@date?：2012?三月?12??10:51:23???????????
*?@version?:?1.0?
?*/??
public?class?ExtendsChildrenSamePackage?extends?ExtendsFather{??
????public?static?void?main(String[]?args)?{??
????????ExtendsFather?children?=?new?ExtendsChildrenSamePackage();??
????????//children.privateValue?=?"no";?無法訪問到??
????????children.defaultValue?=?"ok";??
????????children.protectedValue?=?"ok";??
????????children.publicValue?=?"ok";??
??????????
????????//除了private修飾的方法,其他都繼承到了??
????????//children.privateFunction();??
????????children.defaultFunction();??
????????children.protectedFunction();??
????????children.publicFunction();??
????}??
}??

不同包下的子類 ExtendsChildrenOtherPackage.java?

/**?
?*??
?*/??
package?com.study.featureSecond;??
import?com.study.feature.ExtendsFather;??
??
/**????
?*??
?*?@className?：ExtendsChildrenOtherPackage???
?*?@package?:?com.study.featureSecond??
?*?@Description?：不同包下面的繼承關系????
?*?@author：lgf????
?*?@date?：2012?三月?12??10:50:47???????????
?*?@version?:?1.0?
?*/??
public?class?ExtendsChildrenOtherPackage?extends?ExtendsFather{??
????public?static?void?main(String[]?args)?{??
????????ExtendsFather?children?=?new?ExtendsChildrenOtherPackage();??
????????//children.privateValue?=?"no";?無法訪問到??
????????//children.defaultValue?=?"no";?無法訪問到??
????????//children.protectedValue?=?"no";?無法訪問到??
????????children.publicValue=?"ok";??
??????????
????????//除了public修飾的方法,其他都未繼承到了??
????????//children.privateFunction();??
????????//children.defaultFunction();??
????????//children.protectedFunction();??
????????children.publicFunction();??
????}??
}??

重載和重寫 ExtendsOverRideLoad.java?

/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：ExtendsClass???
?*?@package?:?com.study.feature??
?*?@Description?：重載和重寫????
?*?@author：lgf????
?*?@date?：2012?三月?12??11:00:35???????????
?*?@version?:?1.0?
?*/??
public?class?ExtendsOverRideLoad?extends?ExtendsFather?{??
????@Override??
????public?void?publicFunction()?{??
????????//super.publicFunction();?可以調用父類的方法??
????????System.out.println("Override?publicFunction");??
????}??
??????
????public?void?publicFunction(String?str)?{??
????????//super.publicFunction();?可以調用父類的方法??
????????System.out.println("overload?publicFunction");??
????}??
??????
????public?static?void?main(String[]?args)?{??
????????ExtendsFather?child=?new?ExtendsOverRideLoad();??
??????????
????????//Override?publicFunction??
????????child.publicFunction();??
??????????
????????//child.publicFunction("s");??僅僅只能使用到父類有的方法,重載的方法無法調用??
??????????
????????ExtendsOverRideLoad?childSecond?=?new?ExtendsOverRideLoad();??
??????????
????????//Override?publicFunction??
????????childSecond.publicFunction();??
??????????
????????//overload?publicFunction??
????????childSecond.publicFunction("overLoad");??
????}??
}??

多態?

父類? Animal.java?

/**?
?*?1.?Java中除了static和final方法外，其他所有的方法都是運行時綁定的?
?*?2.?構造方法是被隱式聲明為static方法?
?*?3.?動態綁定?
?*??將一個方法調用和一個方法主體連接到一起稱為綁定（Binding）。??
?*??根據綁定的時機不同，可將綁定分為“早期綁定”和“后期綁定”兩種。??
?*??如果在程序運行之前進行綁定（由編譯器和鏈接程序完成），稱為早期綁定。??
?*??如果在程序運行期間進行綁定，稱為后期綁定，后期綁定也稱為“動態綁定”或“運行時綁定”。??
?*??在Java中，多態性是依靠動態綁定實現的，即Java虛擬機在運行時確定要調用哪一個同名方法。??
?*?
?*??4.?多態總結?
?*??????一、使用父類類型的引用指向子類的對象?
?*??????二、該引用只能調用父類中定義的方法和變量?
?*??????三、如果子類中重寫了父類中的一個方法，那么在調用這個方法的時候，?
?*??????????將會調用子類中的這個方法；（動態連接、動態調用）?
?*??????四、變量不能被重寫（覆蓋），”重寫“的概念只針對方法，?
?*??????????如果在子類中”重寫“了父類中的變量，那么在編譯時會報錯。?
?*??5.?多態詳解?多態是通過:??
?*??????5.1?接口?和?實現接口并覆蓋接口中同一方法的幾不同的類體現的??
?*??????2?父類?和?繼承父類并覆蓋父類中同一方法的幾個不同子類實現的.?
?*?
?*??6.?一個類型引用只能引用引用類型自身含有的方法和變量?
?*/??
package?com.study.feature;??
??
/**????
?*?@className?：Animal???
?*?@package?:?com.study.feature??
?*?@Description?：多態的測試????
?*?@author：lgf????
?*?@date?：2012?三月?12??13:50:36???????????
?*?@version?:?1.0?
?*/??
public?class?Animal?{??
????public?void?eat(){??
????????System.out.println("eating");??
????}??
}??

多態實現?

/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Cat???
?*?@package?:?com.study.feature??
?*?@Description?：貓????
?*?@author：lgf????
?*?@date?：2012?三月?12??13:54:01???????????
?*?@version?:?1.0?
?*/??
public?class?Cat?extends?Animal{??
????public?void?eat(){??
????????System.out.println("eating?fish");??
????}??
}??

/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Dog???
?*?@package?:?com.study.feature??
?*?@Description?：狗????
?*?@author：lgf????
?*?@date?：2012?三月?12??13:55:38???????????
?*?@version?:?1.0?
?*/??
public?class?Dog?extends?Animal{??
????public?void?eat(){??
????????System.out.println("eating?Bone");??
????}??
}??

結果?

/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Main???
?*?@package?:?com.study.feature??
?*?@Description?：多態測試????
?*?@author：lgf????
?*?@date?：2012?三月?12??13:57:11???????????
?*?@version?:?1.0?
?*/??
public?class?Main?{??
??????
????public?static?void?main(String[]?args)?{??
????????Animal?animal?=?null;??
????????animal?=?new?Animal();??
????????animal.eat();//eating??
????????Animal?cat?=?new?Cat();??
????????cat.eat();//eating?fish??
????????Animal?dog?=?new?Dog();??
????????dog.eat();//eating?Bone??
????}??
}??

例子2?

/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Father???
?*?@package?:?com.study.feature??
?*?@Description?：多態????
?*?@author：lgf????
?*?@date?：2012?三月?12??14:53:41???????????
?*?@version?:?1.0?
?*/??
public?class?Father?{??
????public?void?functionOne(){??
????????functionSecond();??
????}??
????public?void?functionSecond(){??
????????System.out.println("Father?functionSecond");??
????}??
}??

/**??*???*/??package?com.study.feature;????/**?????*???*?@className?：Children????*?@package?:?com.study.feature???*?@Description?：測試?????*?@author：lgf?????*?@date?：2012?三月?12??14:55:15????????????*?@version?:?1.0??*/??public?class?Children?extends?Father{??????public?void?functionSecond(){??????????System.out.println("Children?functionSecond");??????}????????????public?static?void?main(String[]?args)?{??????????Father?c?=?new?Children();??????????c.functionOne();//Children?functionSecond??????}??}?
/**?
?*??
?*/??
package?com.study.feature;??
??
/**????
?*??
?*?@className?：Children???
?*?@package?:?com.study.feature??
?*?@Description?：測試????
?*?@author：lgf????
?*?@date?：2012?三月?12??14:55:15???????????
?*?@version?:?1.0?
?*/??
public?class?Children?extends?Father{??
????public?void?functionSecond(){??
????????System.out.println("Children?functionSecond");??
????}??
??????
????public?static?void?main(String[]?args)?{??
????????Father?c?=?new?Children();??
????????c.functionOne();//Children?functionSecond??
????}??
}?