封裝?

Java代碼??

/**?

?*?所謂封裝，就是將對象具有的成員變量和成員函數(shù)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(shí)現(xiàn)封裝有兩個(gè)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(shí)現(xiàn)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(quán)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(jìn)行訪問??

????public?String?getStrValue()?{??

????????return?this.strValue;??

????}??

????public?void?setStrValue(String?strValue)?{??

????????this.strValue?=?strValue;??

????}??

}??

繼承?
父類 ExtendsFather.java?

Java代碼??

/**?

?*?繼承是一種聯(lián)結(jié)類的層次模型，并且允許和鼓勵(lì)類的重用，它提供了一種明確表述共性的方法。?

?*?對象的一個(gè)新類可以從現(xiàn)有的類中派生。?

?*?1.?為什么要使用繼承？?

?*??a.提高程序的擴(kuò)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(gè)包下：?

????公有的受保護(hù)的屬性和方法被子類繼承到了。?

????b、子類和父類不在同一個(gè)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(diào)用父類的那些方法和屬性？?

????a、子類和父類在同一個(gè)包下：?

????公有的受保護(hù)的屬性和方法能被子類調(diào)用。?

????b、子類和父類不在同一個(gè)包下：?

????公有的方法和屬性能被子類調(diào)用。?

????在類和抽象類中，默認(rèn)的就是受保護(hù)的。?

????在接口中，默認(rèn)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?

Java代碼??

package?com.study.feature;??

/**?

*??

*??

*?@className?：ExtendsChildrenSamePackage???

*?@package?:?com.study.feature??

*?@Description?：?同一個(gè)包下面的繼承關(guān)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?

Java代碼??

/**?

?*??

?*/??

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(guān)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?

Java代碼??

/**?

?*??

?*/??

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(diào)用父類的方法??

????????System.out.println("Override?publicFunction");??

????}??

??????

????public?void?publicFunction(String?str)?{??

????????//super.publicFunction();?可以調(diào)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(diào)用??

??????????

????????ExtendsOverRideLoad?childSecond?=?new?ExtendsOverRideLoad();??

??????????

????????//Override?publicFunction??

????????childSecond.publicFunction();??

??????????

????????//overload?publicFunction??

????????childSecond.publicFunction("overLoad");??

????}??

}??

多態(tài)?

父類? Animal.java?

Java代碼??

/**?

?*?1.?Java中除了static和final方法外，其他所有的方法都是運(yùn)行時(shí)綁定的?

?*?2.?構(gòu)造方法是被隱式聲明為static方法?

?*?3.?動(dòng)態(tài)綁定?

?*??將一個(gè)方法調(diào)用和一個(gè)方法主體連接到一起稱為綁定（Binding）。??

?*??根據(jù)綁定的時(shí)機(jī)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(yùn)行之前進(jìn)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(yùn)行期間進(jìn)行綁定，稱為后期綁定，后期綁定也稱為“動(dòng)態(tài)綁定”或“運(yùn)行時(shí)綁定”。??

?*??在Java中，多態(tài)性是依靠動(dòng)態(tài)綁定實(shí)現(xiàn)的，即Java虛擬機(jī)在運(yùn)行時(shí)確定要調(diào)用哪一個(gè)同名方法。??

?*?

?*??4.?多態(tài)總結(jié)?

?*??????一、使用父類類型的引用指向子類的對象?

?*??????二、該引用只能調(diào)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(gè)方法，那么在調(diào)用這個(gè)方法的時(shí)候，?

?*??????????將會(huì)調(diào)用子類中的這個(gè)方法；（動(dòng)態(tài)連接、動(dòng)態(tài)調(diào)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(shí)會(huì)報(bào)錯(cuò)。?

?*??5.?多態(tài)詳解?多態(tài)是通過:??

?*??????5.1?接口?和?實(shí)現(xiàn)接口并覆蓋接口中同一方法的幾不同的類體現(xiàn)的??

?*??????2?父類?和?繼承父類并覆蓋父類中同一方法的幾個(gè)不同子類實(shí)現(xiàn)的.?

?*?

?*??6.?一個(gè)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(tài)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(tài)實(shí)現(xiàn)?

Java代碼??

/**?

?*??

?*/??

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");??

????}??

}??

Java代碼??

/**?

?*??

?*/??

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(jié)果?

Java代碼??

/**?

?*??

?*/??

package?com.study.feature;??

??

/**????

?*??

?*?@className?：Main???

?*?@package?:?com.study.feature??

?*?@Description?：多態(tài)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?

Java代碼??

/**?

?*??

?*/??

package?com.study.feature;??

??

/**????

?*??

?*?@className?：Father???

?*?@package?:?com.study.feature??

?*?@Description?：多態(tài)????

?*?@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");??

????}??

}??

Java代碼??

/**?

?*??

?*/??

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??

????}??

}?

轉(zhuǎn)載于:https://www.cnblogs.com/caimuqing/p/5398415.html

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