理解什么是继承
首先我们知道，面对对象有三大特征：
继承是利用现有的类创建新类的过程，现有的类称作基类（父类），创建的新类称为派生类（子类），派生类可以拥有所有基类的非私有的属性和方法。
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miaR/rSwGoaLLctZTY2m37v6qZNblxKo+eqvNMp9Ruu9bBgR0BCAkaZECcdjwk+uc/BskD/+6jau5nYyp3rbGjvhpA1pxVxpjU407JsOKp+VxBKp0rO/Z6OevSwY4AhAQNMiB5djwkOvv+98kzX/cy5ZtVuSXsyBrzzKY3Ai/3FTnQzD2/gRGAOkrugqiq+1dNL2rlJWZk2ZH/Mgg1qhoW2BEIBQ0yIB52PCSaf/NB8tjXuky5zMpdLGgyKZMFwbpSB/C8FYfA9M7J9AHuSS6kCbJQtKqWDs+yEaf2Fwry1NJCw2GB/udy0Wr1wI5AKP4N8vDj5OC6yr2rNZc/f0iHH2cWPzv+8ObVf/d+F/+i22/T09P6K7di9LAsVEmvEcOfW/M6lFxzl6AbjwvP0GFtW6/LkWUhO/IJo4jGY4ut1UU9d/MQBewIhLJZdtyEkmvHQ6LjF2dVLFO+WW8b1oYaZuNORf1fPdd8UdsrurMYdUOHNYo6Z9bkUta2/3Amb2yZBcejGHcEIBiwYx12PCT6269HyRTWNS1TvllvG6OPNL2boxo+bLfDyMxTjapL038lNpZfVsTJv8s/JM09npd0z1ooQDKwIxBKcTv++/Bjn7d/uXL84mz6y7f1ln8dffLvw49Ll59PPvX8sX//+avk+X/zQZ2VWzvpxbjZInoIyBpw9IhOp/Fq42GLpyBzMx2taf4O+DlkwYFjVgKJcGBHIBRhdty28vPJp0kVHH1SW+XWi3Wfiqz8DX3+Tq9nn4wzGMSpgVmLmrLD+NK566A61qVjfLas4ks7zjabmbNvHEEhH1loYq0cYEcgFNix7vKfv3SSWgi7TLn8tw0nG6Snk2TlbwwG9pSJTqfAhEwO4KKIRiNqt8Ns8+SzRA6vgOMmipYi4CzdWufHRhG12xszQwd2BEKBHesuP7x59eze1bgWwi5TLvxtw2mIal6o/6YTKk1QDyJVdOUZPKVzKpSHVsx2YFG5ZwO1nHN2DLgn2doNyz8knTfJf3aI3ZqDgR2BUGBHAeXo9dNkCuvub4ItUy72bcNTV3j4MIrM/EVH0UU4mVC3WyzySy8CwJopHUGyjdwJ/hz1ek6fcS8PpLqFs66YfsgygR2BUGBHGeXk2aM3t9+O6+IPvw2zTLnMt8147OWzUDtypK9u1RjrrVxGRHqTZCv8ozzTORxTeFRY6b5bDj0lp3nAjkAosKOYMv3l28DLlG/022YdduRwyqoxfS3WQvGWpxpJC1s9Ozy5t9l4CJz7b6CvQ2TE4rmr1tUF7AiEAjtKKrMfP0tqZPVlyjf6bZNrR2O5gFw4kHKM+emCbLWo3c7XmFJj+py8JVa/H/8EfTKR53wZPp4fgrHTlqN0uzQcJr9a7Bgk7AiEAjsKK9F3HyWV8uNnFVWuQNx21LfR8N8KynNkMWsE1LgQq9TRTcozj8qFcdbY0XpvaiqvFZ77CjsCUADYUV55+vX7yRTWVZYpl/y20WOaFYtjXyd9XmuhGTdG0kinY15Cndm9pZTC2A/Lf9kdupysNBgsxZr86EYjrxhU3YDnLNnqgR2BUGBHeeWHN69e/OG3cb2sskz5dr5tomhJvZ4KsTKbxf2TBur8/p26HEEK3CKjdmBHIBTYUWQ5efbof7u/iavmi3dKTmHdzreN2sgCbAqwIxAK7Ci1nJ6Pkyms966WWaYcbxsgH9gRCAV2FFz++Y9BUkF//nCNlQtAXcCOQCiwo+zyr6NPkjoqukw53jZAPrAjEArsKL7Mv/kgqaZHf1xL5QJQF7AjEArsKL788ObVf/d+l+R4/HoUvnIBqAvYEQjFv0FebrQ0+/Gz2oWxbeX4xVmZZcrxtgHygR2BUPwb5J8/VEc++ul27bbYtrKU4PHlu74JHnjbAPlsrR3nF/T8Zd03ARzAjuLL0eunr758t3DgWKhyAagLIXbcP6adPTqbV3fFK9foyjXafRDMkWdzenwe4DzzC9o/pumTkt/d2aO7+zmHXb9JV67R3f2c3342pxt36MadSuslAXaUXcy9kf0HHQtVLgB1IcSO84tYV9dv0vyi5ElOHtKVa3Tjjpfw1OWuXKP7ByUvxzw+D3m2s3lyttJlZ891CT7swLkQmH4n7iPXAuwou/x6+dgLT1gtVLkA1IUQO9KyY0oHYXf34zPkxl4+FnFzNqedPYuZVoy02Em7Dwp/9+DU6wHyra7vTgIAOwou/76cJ0y3WnTy6RorF4C6kGNHItp9EOB17KnYEhc6m9P9g7hb0ij7x0shr6OX9eCU9o9zrrK6Hd2GzrLjyUO6fjO5PdgRxVqWFsopt9ejgLcNADmIsiO/jnN7/By9r/vHXicp+t4/OKXrN+nuPh2cxuZzqIj/KavcuOP6dXXZkf86uXKNnr+EHVEsZfrLt8kiq1+/v/bKBaAuRNmRiE4e5ljtxp34lZ0lyOcvl2LHg1P7Ca3v/ekTOnnoe6ur2PH6zczB0SDjjuXsyM9W3RvsiGKUvz49fXP77bhe/vDbMuuPF61cAOqiAjtOnwR43VuLQ5Dq/a7mf+4fx9LVC5+EP+ExS0dgp+NjR+Of+HPHXwCeAbQVNS8pd84q//b7B4mk+a8KHouFHVH0spT4/8U79OKsisoFoC6qiR1PHsZ9klmF39fuw/Ry8jB/duv9A7q7T2dz+2BhVtnZ85oWJMeO8wu6f5AIz30kW1D/+4C0P2I4erbaUV1o9am5+cCOksrSonGr7HtctHIBqAshPas84lViwqcxl8Q4bVYgtXpUlFbg7oP4hOuz4+PzOMx1+D5LXWdz2n2w9LcIP/aTh0t+NYJpjrC567UKQcKOksrTr98nTm38+avqKheAumiAHUlL5NC/fvKQdh9kRoGF7Di/WFKFu9y4k8wMWtGOz18m0nJcjn2mStZPnj6hG3eW7MjXOnm4ZD6fcne/fGaqF7CjmBJ991FSHT/drrRyAagLaXYsDcdSnOm4s+dKZywaOxqdw7osjd7g6ZNEaWvqWS03NqnuSrcjEe0f0/2D5IR6nijGHVEOiWY/fpbUxfe/r7pyAagLIXZUbrt+0/6vPour8bCZOsnjc7p+09X7t+J7n6NDa7wbtmc1PZM2y467D2hnzz4blocbDTsqeJkh61Vgx60tf//5q6QivvmghsoFoC6E2NGzN88tSNU3qOy4+yBnUboV3/v6sN+67ainIXp27abhZX2sdlSPzni8sOOWl7/9epSkNt67Wj5/Y5XKBaAuJNjRP8PPPRNk+oR2H9D0SRwnuRMzst77vOKrw8TpHJWdvSUTr8mOjmPIuYwc/6gr15bmrOpnS/dCw47bXE6ePVrK3/Dcmip45QJQFxLsqLr1soTEb3P/d7QaYNs/Lhx1eYaqxgSWdBxZrx1zZzYZdrx/YNrduIr+5DmXdO0Ut+PTr9//9+HH5cqjn25Pf/m23lK7EbkcvX764g+/TfI3/LemCl65ANSFBDvyDBfra7dEBMNnm1/QyUOLLdQVPXfzMNAHONlG+sxSlXRR2o58/tI9q0XtuH9sv5/0k+d7K7fBVjGK2xHFXX7984c+avzhzauLP70Xf+vzt+h8XGflAlAXEuzInZNW0rZwowzkmK2qdy2W6DNUUtzZMxXIgtRzCkvYMd1BWtSOuYkWhh0V+jyjVQLrYMCONdnxP3/pJN/6x6DmygU+tFrUwsMMTe12TC/RYsC28FwBNfdg1ljuimuOm5lf2FcDuHKZTb+6Hfm7Z/N4MJWx9qzOL3yzRa12VJfOylpJr1W09i2R/Rvkoz/S4ccrlXtXay48wle3Hf919EnylaNP6q9c4APsuA5qt2NupqM10z8LVksWHDhmZY84MCbsWBWoHLaKHfUHwsu2GWbSl4Q1/olDQEdsl2VHg42ZlQPc/HTb045LW1P9pbPGW0LlhgV2XAf12tEnq51t4djUwuh7dASFfGSJdV7UZBxesm5N66yqq6gJt6vMKspdCQF23Bb87Hh6Pk7yN/70Xsj8jTSo3LDAjuugXjv6LJHDk18czC+SfD6He6yTY+cXdP1m/gyd9Orba7KjOkBdKOv5GH9VPD5PBil9/uCAHbcLDzuePHu0tDVV2PyNNKjcsMCO66BGO7Kr3Bti5EZCTNb6bQruU00nTXKXqWOF0vQXfeyYVbLU9fh86U487ag6WlVQCzsCkzw7Hr1+upTaGDx/Iw0qNyyw4zqoy44sJHeCP7+gfWbQuBP+VI9l1uV4clB6r4/pE/seIOuIHZXgeUw0145q3JGHIfUVU2FHEOO04w9vXj27dzV+1J+/Rb8eVXFLqNywwI7roC476qNrDny6IhnH/B1lHfdbXk/J8GEVO2ZNmVHdyGxi3Y5ZW1bt7C0lY3BEDjuCGKcd5998kDzq1bem8gSVWxolQv8CSlOLHT3VSJoefLYj1tPzdTj33+D5S5o+sWQv5Ea0Ch87GnN/3EkXHL/yCKhuR/7XnT3LSfRu6nXbcX5Buw/sG2qGBC/QUGTb8ez73yfP+cfPqrslVG5pYMfKqN6OSo3pcUR+rd/dj9/++vqrPova8MEsDz5nblERmLHkjRuHHf1TD3XUxCLdaoU29ppf0POXhXtW1XJC6XTGrHxHPU5d7wbIeIGGIsOOS1tTffdRpbeEyg0LRLgOqrQjjzU6XtzWFVs838LW2NHqQjU+Z4Xnvq5ixxJYlwL3tOPZ3NLv6rh/w46ef0BYyxpXzMELNBQ2O/7956+S/I2v36/6llC5YYEd10FldlQuce8qpTB2wPDpgFXML+juPt0/WAo0ORw8OPUKQNXVfabIhrWjsrLxcArFjty5eiVvrQPPntWawQs0FCk7/u3XoyR/Y+93601ttILKDQvsuA6qsaNSlH+c4bPgS+08Pqf94zBqVAuXp/9uOHlI+8cFlkpXPcm5uZtKupKfLRFeoOFYtuPxi7Ol/I0XZzXcEio3LLDjOqgx3xEAF2iQodDs+MObV0tbUz31W9o/OKjcsMCO6wB2BEJBgwyFZselral++ba2W0LlhgV2XAewIxAKGmQoLu2YTMO51aKfbtd5S6jcsMCO6wB2BEJBgwzFpR2TcvhxzbeEygXygR2BUNAgQ2HY8ZsP6r4hVC7YBGBHIBQ0yFDodrx3tYb8jTSoXCAf2BEIBQ0yFGzHL99d+9ZUnqBygXxgRyAUNMhQKDvefruKrak8QeUC+cCOQChokKH46TZ9/hadj+u+Dw1ULpAP7AiEggYZip9u06M/1n0Ty6BygXxgRyAUNMhQSJiGY4DKBfKBHYFQ0CAbDCoXyAd2BEJBg2wwqFwgH9gRCAUNssGgcoF8YEcgFDTIBoPKBfKBHYFQ0CAbDCoXyAd2BEJBg2wwqFwgH9gRCAUNssGgcreKKKLFou6bKA7sCISCBtlgmlG5/T71euaHsxmNxxRFXmcYjeKtGWez4HdnZzikbre6yynUb+z1NsyRsCMQChpkg5FcuVFEgwGNlxfeGwyo1aLJZOkw9dJvtZZcyMLr9/OvxQe32xWZg2+73fZVuJXxmFot6nS8bpsf1GBQ/orVAzsCoaBBNhjJlTubJW/zdJlO48OGw/iT0Wjp6yw8PtJB9bEjEU2nlp9Tgn4/Pon+R4MVdVi3W/5atQA7AqGgQTYYyZXLdmTtsU700KfTiT80KCS8WuxIRL1e0tu5Cp6WDXKt6oEdgVDQIBuM5MpN25HDRO5FTB/DbIQdHfdvHObufc0KoA1gRwBCggbZYCRXbtocKkzUA0c1DJkOHCm0HWczGg7tkdlkQsNh+bHD8ThHaRwcOy6xWCzFjqOR/ZxWO04m5uCuNGBHIBQ0yAYjuXINO/I0Fl1gjjkmq9tRl7F7ENSw12SSf3C54hakCqmjiIZDGg5j7+qFz8Of8Jhlp5P/lOoCdgRCQYNsMJIr17CjmpypzyhRn+gdrTpuO3JA5lOm0+RmOh27cgy7jMfU75tHWkXlPkwvngkqgwH1+zSbUbtd4Dd2uyvNDForsCMQChpkg5FcuYYdu11qLU/LVIbLCoSW8UoAAAVjSURBVHp0O45GNBy6rpVWKV9dfdExQGjtrsyF5+OUG+kcj6ndtv+oXi8ziaXcrdYO7AiEggbZYCRXriGkVova7eRf9d7LbpdGo/xQydF56LCjuro0O5KWyKGfYTymXi8zCoQdAQgJGmSDkVy5upBmM+p2l0IlvWtUTens9+NjVD8kH8Bdl5NJZso825G7Liuz4yrwHwQcUne7rnRG2BGAkKBBNhjJlWsIaThMZt/wiKMj/Co3Kyfr6sHtqMSmR8M6amZNbnY/B9DqPNMptduudXBgRwBCggbZYCRXbtpP7XY8otbtUq+X479CdkxHcnx11UsZ3I6ek2VyBalCZGXHXi9nXTrYEYCQoEE2GMmVmxaSmpijvEjL/ptMqNtdytsLZUf19bB29MkPUSV3QdTJhHq9uNPYPbbquFXOlsmVcS3AjkAoaJANRnLlpoXEHYlq+NDwnzFLpYQd9RG7tdqRe4atNuLU/kLnVAsjDIeJ6csVgYKEHYFQ0CAbjOTKtQpJ/yTtP56lMp0Ws2PaRmu1I4vcOkuIr1XonHzCKKLx2PKr1UU9d/MQBewIhIIG2WAkV65VSNy5Ss40jNxRSQN1pD4n1vh6WDuqr2RNLuUQ2b3CnI66W8dsVY5Hi96qBGBHIBQ0yAYjuXKtQtIHCB3Lv6ksDk878oX0TkX+uoq0AtqR5Ze1uilf2n/509zjeUFan90upQE7AqGgQTYYyZVrFZLqO1VBktV/UVR43DG99QelcjwC2jE309Ga5u8gnY5iwIFjVgKJcGBHIBQ0yAYjuXL1iZ2G8LLGHXX87ah6a41uyTXZ0WfLKtanY4BwNjNn3ziCQj6y9EYi9QI7AqGgQTYYyZWblfbAAVAQO3JcZczVVEbha4Wyo88SOTy3yE0UxV5369Y6PzaKqN3emBk6sCMQChpkg5FcubqQptNEjfxCD2LHrG5JpTF2XhA7sqjcu2G0nHN2DHhA0foz2f3pvEnOcRS7NQcDOwKhoEE2GMmVawhpOjXf40HsqAK1LOdxd+XqdmQbuRP8+UKe02d8NurKuiLPD3JvYFI7sCMQChpkg5FcublDdKvbMStw5FCVL527uk2uHd37baVvyTOdwzGFR4WV7hvj0FNymgfsCISCBtlgJFduBXbkrkU1bVUt4a1vTczRau7ux267eKqRtIFJzw5PHqQ0fibn/hssFjSZxHfOZvUJamsEdgRCQYNsMJIrt4Qd1UoxWf9qoNzAnYrp6FBXyyo9q0qN6XFEjlD7fXPNgZZzwmr66vrP5NPmFrXhF4ePYscgYUcgFDTIBiO5csvZMb3KqDWNQQ25paMlfRao/sVyduSxRkc3KWdblgvjrLGj1YWDQeYfCvyrYUcACoAG2WAkV66/HQ3/sZOyNKPyGayTQqOIej3Lt4wNrXQmE/siNer23FtK8RmyYtZc1LbPg8FSrMnh4GjkFYOqG/CcJVs9sCMQChpkg5FcuQ4h8QFq56Y0WStxK8bjAkuYKvQ+Wx+Un/z3u+AIUuAWGbUDOwKhoEE2GOGVuxG56mDdwI5AKGiQDQaVC+QDOwKhoEE2GFQukA/sCISCBtlgULlAPhY7oqCIKqB5oHKBfC5bad1vQBSUrAKaByoXyOeyldb9BkRBySqgeaBygXwuWymaKQCgKmBHIB/YEQBQNbAjkA/sCACoGtgRyAd2BABUDewI5AM7AgCqBnYE8oEdAQBVAzsC+cCOAICqgR2BfGBHAEDVwI5APrAjAKBqYEcgH9gRAFA1sCOQD+wIAKga2BHIB3YEAFQN7AjkAzsCAKqm9qXtUVC8C+wIAKiKut93KCj+BXYEAFRF3e87FBT/8v8kcR7u+jU3qgAAAABJRU5ErkJggg==" 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例如，我们可以有一个类“人”，而我们要创建一个新的类“学生”，学生也是属于“人”的一种，有“人”这个类的一些共通属性行为，我们就可以把“学生”这个类继承自“人”，而还有“小学生”、“中学生”、“大学生”，他们都属于学生，我们可以让他们继承自“学生”类。
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" alt="" width="278" height="199" />
在继承中，最高层的应该是最具有普遍性的、最符合一般情况的，往下一层，都应该比上一层更具体，在继承中子类能够自动共享基类中的成员属性和成员方法。
如何使用继承
在Java中，要继承，需要使用extends关键字，继承的语法格式如下：
[访问修饰符] class 子类名 extends 父类名 {
成员列表
}
如
public Student extends Person{
......
}
例子：
按照上面的举例，我们先定义一个Person类
public class Person{
public String name;
public int age;
public void sleep(){
System.out.println("我正在睡觉");
}
public void eat(){
System.out.println("我正在吃饭");
}
}
对于“人”来说，人都有一个名字，都有年龄，能够睡觉，也可以吃饭。
而我学如果此时需要有一个学生类，学生也属与人，学生也都有人的特征，此时我们便可以使学生继承于人。
public class Student extends Person{
public String sid; //学号
public String cls; //班级
public void study(){
System.out.println("我正在学习");
}
}
对于学生来说，学生有自己的学号，有自己的班级，还有学习等等功能。
public class Test{
public static void main(String[] args){
Student stu = new Student();
stu.name = "张三";
stu.age = 20; //我们可以为Student类型的对象设置name和age，因为S图等继承自Person，所以也拥有Person类的属性和方法。
stu.sleep();
stu.eat(); //我们也可以使用Person类的方法。
stu.sid = "S20150101001"; //当然，我们也可以使用Student自己的属性和方法
stu.cls = "1001";
stu.study();
Person p = new Person();
p.study(); //错误，父类不可以使用子类的属性和方法。
}
}
当然，如果还需要有大学生等，我们可以定义大学生，使大学生继承自学生类，大学生便可以拥有学生类和“人”类的属性和方法。
需要注意的是，Java中的继承是单继承，也就是说，只能继承一个父类，如果Student继承了Person类，那就不能再直接继承其他的类。
继承中的构造方法
需要注意的是，父类中的构造方法是不能被继承的。
同时需要我们注意的是，在对象的构建过程中，会先构建出父类，在构建出子类，这个比较好理解，就想在现实生活中一样，只有先有父亲，而后才有儿子一样。
例如：
class ParentClass { //定义父类
public ParentClass() { //构造方法
System.out.println("这是父类的构造方法。");
}
}
class ChildClass extends ParentClass { //子类继承于父类
public ChildClass() { //构造方法
System.out.println("这是子类的构造方法。");
}
}
public class ConstructorTest { //该类用于容纳main方法
public static void main(String[] args) {
ChildClass cc = new ChildClass(); //实例化子类对象
}
}
执行输出：
这是父类的构造方法。
这是子类的构造方法。
因此：
- 当实例化子类的对象时，必须先执行父类的构造方法，然后再执行子类的构造方法。
- 如果父类还有更上级的父类，就会先调用最高父类的构造方法，再逐个依次地将所有继承关系的父类构造方法全部执行。
- 如果父类的构造方法执行失败，那么子类的对象也将无法实例化。
super关键字
在Java中，用super关键字可以对父类进行操作。
super主要有两种用途：
Java中继承的特点与继承作用
特点
继承是单向的，子类可以访问父类中的成员，但父类无法访问子类的成员。
Java中只允许单继承，一个子类只能拥有一个父类。
作用
引入继承，实现了代码重用；
引入继承，实现了递增式的程序设计。
能减少代码和数据的重复冗余度，并通过增强一致性来减少模块间的接口和界面，从而增强了程序的可维护性；
能清晰地体现出类与类之间的层次结构关系。