Java学习day011（oop）：

迈不过友情╰ 2023-07-25 12:45 34阅读 0赞

#### 1.方法的重写（override）：重新写/覆盖 ####

##### 1.1 发生在父子类中，方法名相同参数列表相同（签名相同），方法体不同； #####

##### 1.2 重写方法被调用时，看对象的类型（new谁调谁）； #####

##### 1.3 重写需遵循“两同两小一大”的原则————了解，一般情况一模一样； #####

###### 1.3.1 两同：方法名、参数列表相同 ######

###### 1.3.2 两小： ######

①派生类方法的返回值类型要小于或等于超类方法；  
void时必须相同  
基本类型必须相同  
引用类型时，必须小于等于。——（程序认为超类大，派生类小）  
②派生类方法抛出的异常小于或等于超类方法；

###### 1.3.3 派生类方法的访问权限大于或等于超类方法——访问修饰符时 ######

#### 2.重写和重载的区别————常见面试题 ####

##### 2.1 重写（override） #####

**Ⅰ. 发生在父子两个类中，方法名、列表参数相同，方法体不同；**  
Ⅱ. 遵循“运行期绑定”，看对象的类型来绑定方法；  
ⅢⅣ

##### 2.2 重载（overload） #####

**Ⅰ. 发生在一个类中，方法名相同，参数列表不同，方法体不同；**  
Ⅱ. 遵循“编译期绑定”，看参数/引用类型来绑定方法；

Aoo o=new Boo();
    override______Boo
    overload______Aoo

#### 3. package和import ####

#### 3.1 package ####

作用：避免类的命名冲突  
包名可以有层次结构，类的全称是：**包名.类名**  
同包中的类不可以同名，不同包的类可以同名；  
建议包名的所以字母都是小写

起名的建议
    域名反写.项目名称.模块名称.类名
    com.taobao.aporject.studentmanager
    com.taobao.aporject.teachermanager

##### 3.2 import #####

同步中的类可以直接访问  
不同包内的类不可以直接访问，若想要访问只有两个方式  
①先import声明类再访问类————建议  
②写出类的全称————太繁琐，不建议

#### 4. 访问控制修饰符 ####

数据（变量）私有化（private）  
行为（方法）公开化（public）

##### 4.1 public ：公共的，任何类都能访问 #####

##### 4.2 private ：私有的，只能本类使用 #####

##### 4.3 protected ：受保护的，本类、派生类、同包类可用 #####

##### 4.4 默认：什么都不加，本类、同包类可用 #####

##### 说明： #####

①类的访问权限只能是public和默认的  
②类中成员的访问权限如上四种都可以  
**一般类都定义权限为public；**

#### 5. final：最终的、不可改变的，单独应用几率低 ####

#### 5.1 修饰变量：变量不能被改写 ####

#### 5.2 修饰方法：方法不能被重写 ####

#### 5.3 修饰类：类不可被继承，但可以继承未被修饰的类 ####

Swing相关的东西————操纵窗口（目前已经不适应了）

1.  import ——JFrame+JPanel
2.  设计world类来继承JPanel
3.  复制粘贴到main中JFrame frame = new JFrame();  
    World world = new World();  
    frame.add(world);
    
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         frame.setSize(WIDTH, HEIGHT);
         frame.setLocationRelativeTo(null); 
         frame.setVisible(true); 
         
         world.action();
4.  main中 frame.setSize();的参数改为400,700；  
    **练习**

/*5package day05; public class Person { protected int age; protected String address; protected String name; public Person(String name,int age,String address){ this.address=address; this.age=age; this.name=name; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address); } } package day05; public class Doctor extends Person{ private String leavl; public Doctor(String name,int age,String address,String leavl){ super(name,age,address); this.leavl=leavl; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"职称："+leavl); } } package day05; public class Student extends Person{ private int stuId; public Student(String name,int age,String address,int stuId){ super(name,age,address); this.stuId=stuId; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"学号："+stuId); } } package day05; public class Teacher extends Person{ private int slary; public Teacher(String name,int age,String address,int slary){ super(name,age,address); this.slary=slary; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"工资："+slary); } } package day05; public class Test { public static void main(String[] args) { Person []ps=new Person[6]; ps[0]=new Student("zw",22,"lg",20192020); ps[1]=new Student("zs",22,"lg",20192020); ps[2]=new Teacher("wq",33,"lg",5000); ps[3]=new Teacher("ew",42,"lg",4000); ps[4]=new Doctor("xxc",52,"lg","s"); ps[5]=new Doctor("sda",62,"lg","a"); for(int i=0;i<ps.length;i++){ System.out.println("name:"+ps[i].name); ps[i].sayHi(); } } } /*4 package day05; public class Person { protected int age; protected String address; protected String name; public Person(String name,int age,String address){ this.address=address; this.age=age; this.name=name; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address); } } package day05; public class Doctor extends Person{ private String leavl; public Doctor(String name,int age,String address,String leavl){ super(name,age,address); this.leavl=leavl; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"职称："+leavl); } } package day05; public class Student extends Person{ private int stuId; public Student(String name,int age,String address,int stuId){ super(name,age,address); this.stuId=stuId; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"学号："+stuId); } } package day05; public class Teacher extends Person{ private int slary; public Teacher(String name,int age,String address,int slary){ super(name,age,address); this.slary=slary; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"工资："+slary); } } package day05; public class Test { public static void main(String[] args) { Person []ps=new Person[6]; ps[0]=new Student("万万",22,"lg",20192020); ps[1]=new Student("按时",22,"lg",20192021); ps[2]=new Teacher("斜齿",33,"lg",5000); ps[3]=new Teacher("深度",42,"lg",4000); ps[4]=new Doctor("反复",52,"lg","s"); ps[5]=new Doctor("国防",62,"lg","a"); for(int i=0;i<ps.length;i++){ System.out.println("name:"+ps[i].name); ps[i].sayHi(); } } } /*3 package day05; public class Person { protected int age; protected String address; protected String name; public Person(String name,int age,String address){ this.address=address; this.age=age; this.name=name; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address); } } package day05; public class Doctor extends Person{ private String leavl; public Doctor(String name,int age,String address,String leavl){ super(name,age,address); this.leavl=leavl; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"职称："+leavl); } } package day05; public class Student extends Person{ private int stuId; public Student(String name,int age,String address,int stuId){ super(name,age,address); this.stuId=stuId; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"学号："+stuId); } } package day05; public class Teacher extends Person{ private int slary; public Teacher(String name,int age,String address,int slary){ super(name,age,address); this.slary=slary; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"工资："+slary); } } package day05; public class Test { public static void main(String[] args) { Person []ps=new Person[6]; ps[0]=new Student("如图",22,"lg",20192020); ps[1]=new Student("地方",22,"lg",20192022); ps[2]=new Teacher("从v",33,"lg",5000); ps[3]=new Teacher("更换",42,"lg",4000); ps[4]=new Doctor("即可",52,"lg","s"); ps[5]=new Doctor("即可我",62,"lg","a"); for(int i=0;i<ps.length;i++){ System.out.println("name:"+ps[i].name); ps[i].sayHi(); } } } /*2 package day05; public class Person { protected int age; protected String address; protected String name; public Person(String name,int age,String address){ this.address=address; this.age=age; this.name=name; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address); } } package day05; public class Doctor extends Person{ private String leavl; public Doctor(String name,int age,String address,String leavl){ super(name,age,address); this.leavl=leavl; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"职称："+leavl); } } package day05; public class Student extends Person{ private int stuId; public Student(String name,int age,String address,int stuId){ super(name,age,address); this.stuId=stuId; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"学号："+stuId); } } package day05; public class Teacher extends Person{ private int slary; public Teacher(String name,int age,String address,int slary){ super(name,age,address); this.slary=slary; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"工资："+slary); } } package day05; public class Test { public static void main(String[] args) { Person []ps=new Person[6]; ps[0]=new Student("如图",22,"lg",20193020); ps[1]=new Student("覆盖",22,"lg",20191020); ps[2]=new Teacher("不能",33,"lg",5000); ps[3]=new Teacher("喝酒",42,"lg",4000); ps[4]=new Doctor("即可",52,"lg","s"); ps[5]=new Doctor("与",62,"lg","a"); for(int i=0;i<ps.length;i++){ System.out.println("name:"+ps[i].name); ps[i].sayHi(); } } } /*1 package day05; public class Person { protected int age; protected String address; protected String name; public Person(String name,int age,String address){ this.address=address; this.age=age; this.name=name; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address); } } package day05; public class Doctor extends Person{ private String leavl; public Doctor(String name,int age,String address,String leavl){ super(name,age,address); this.leavl=leavl; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"职称："+leavl); } } package day05; public class Student extends Person{ private int stuId; public Student(String name,int age,String address,int stuId){ super(name,age,address); this.stuId=stuId; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"学号："+stuId); } } package day05; public class Teacher extends Person{ private int slary; public Teacher(String name,int age,String address,int slary){ super(name,age,address); this.slary=slary; } public void sayHi(){ System.out.println("我的名字："+name+"；年龄："+age+"；家住："+address+"工资："+slary); } } package day05; public class Test { public static void main(String[] args) { Person []ps=new Person[6]; ps[0]=new Student("请问",22,"lg",20192023); ps[1]=new Student("撒",22,"lg",20192024); ps[2]=new Teacher("现在",33,"lg",5000); ps[3]=new Teacher("反倒",42,"lg",4000); ps[4]=new Doctor("二",52,"lg","s"); ps[5]=new Doctor("如图",62,"lg","a"); for(int i=0;i<ps.length;i++){ System.out.println("name:"+ps[i].name); ps[i].sayHi(); } } }