Java学习_day009面向对象（oop）：对象和类（下）

刺骨的言语ヽ痛彻心扉 2023-07-24 11:33 61阅读 0赞

方法的签名：方法名+参数列表  
在一个类中不允许出现多个方法签名重复的情况

### 一、方法的重载（overload） ###

1.  发生在同一个类中，方法名称相同，参数列表不同，方法体就不同。
2.  编译器在编译时会根据方法的签名自动绑定调用的方法。

System.out.println();
    System.out.println(" ");
    System.out.println(55);
    System.out.println(5.3);
    System.out.println('6');
    //println()就使用了重载的方式，可以输出多种数据类型

![方法重载的标志][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70]

### 二、构造方法 ###

1.  给成员变量赋值初始值
2.  与类同名，没有返回值类型（连void也没有）
3.  创建对象时被自动调用
4.  若自己没有定义构造方法，则编译器默认提供一个无参数构造方法，若自己定义了，则不再默认提供
5.  构造方法可以重载  
    ![方法构造][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 1]

//创建了一个学生对象
    //给成员变量赋默认值
    //调用构造方法new Student（）；小括号是方法的标志
    Student zs=new Student("张三",25,"廊坊");

### 三、this :指代当前对象，哪个对象调用方法它指的就是那个对象 ###

只能用于方法中，方法中访问成员变量之前默认有个（**this.**）  
![this.][]

![在这里插入图片描述][20200411111040652.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 2]  
Java规定：成员变量和局部变量可以重名——在使用时采取的是就近原则；  
当成员变量与局部变量重名时，此时若想要使用成员变量则**this**不可省略  
成员变量——整个类都可应用  
局部变量——独属于方法应用  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 4]  
**常规写法：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 5]  
![在这里插入图片描述][20200411141056363.png]

#### 内存管理——null ####

由jvm来管理的

1.  堆：储存new出来的对象（包括成员变量）
2.  栈：局部变量（包括方法的参数）
3.  方法区：.class字节码文件（包括方法）  
    ***练习***

/*5 package oop.day02exer; public class Aoo { void show(){} void show(int age){} void show(int age,String name){} void show(String name,int age){} void show(String name){} } package oop.day02exer; public class OverloadDemo { public static void main(String[] args) { Aoo o=new Aoo(); o.show(); o.show(4); o.show(4,"Asd"); o.show("asd"); o.show("sda,4"); } }*/
    /*4 package oop.day02exer; public class Aoo { void show(){} void show(int age){} void show(int age,String name){} void show(String name,int age){} void show(String name){} } package oop.day02exer; public class OverloadDemo { public static void main(String[] args) { Aoo o=new Aoo(); o.show(); o.show(5); o.show(5,"Asd"); o.show("asd"); o.show("sda,5"); } }*/
    /*3 package oop.day02exer; public class Aoo { void show(){} void show(int age){} void show(int age,String name){} void show(String name,int age){} void show(String name){} } package oop.day02exer; public class OverloadDemo { public static void main(String[] args) { Aoo o=new Aoo(); o.show(); o.show(6); o.show(6,"Asd"); o.show("asd"); o.show("sda,6"); } }*/
    /*2 package oop.day02exer; public class Aoo { void show(){} void show(int age){} void show(int age,String name){} void show(String name,int age){} void show(String name){} } package oop.day02exer; public class OverloadDemo { public static void main(String[] args) { Aoo o=new Aoo(); o.show(); o.show(6); o.show(7,"Asd"); o.show("asd"); o.show("sda,8"); } }*/
    /*1 package oop.day02exer; public class Aoo { void show(){} void show(int age){} void show(int age,String name){} void show(String name,int age){} void show(String name){} } package oop.day02exer; public class OverloadDemo { public static void main(String[] args) { Aoo o=new Aoo(); o.show(); o.show(7); o.show(7,"Asd"); o.show("asd"); o.show("sda,74"); } }*/

/*5package oop.day02exer; public class Student { String name; int age; String address; Student(String name,int age,String address){ this.name=name; this.age=age; this.address=address; } void study(){ System.out.println(name+"studing.."); } void sayhi(){ System.out.println("hi,name:"+name+";age:"+age+";address:"+address); } } package oop.day02exer; public class Student_Test { public static void main(String[] args) { Student ww=new Student("wangwu",54,"sh"); ww.sayhi(); } }*/
    /*4 package oop.day02exer; public class Student { String name; int age; String address; Student(String name,int age,String address){ this.name=name; this.age=age; this.address=address; } void study(){ System.out.println(name+"studing.."); } void sayhi(){ System.out.println("hi,name:"+name+";age:"+age+";address:"+address); } } package oop.day02exer; public class Student_Test { public static void main(String[] args) { Student zs=new Student("zhangsan",22,"ls"); zs.sayhi(); } }*/
    /*3 package oop.day02exer; public class Student { String name; int age; String address; Student(String name,int age,String address){ this.name=name; this.age=age; this.address=address; } void study(){ System.out.println(name+"studing.."); } void sayhi(){ System.out.println("hi,name:"+name+";age:"+age+";address:"+address); } } package oop.day02exer; public class Student_Test { public static void main(String[] args) { Student ls=new Student("lisi",33,"wh"); ls.sayhi(); } }*/
    /*2 package oop.day02exer; public class Student { String name; int age; String address; Student(String name,int age,String address){ this.name=name; this.age=age; this.address=address; } void study(){ System.out.println(name+"studing.."); } void sayhi(){ System.out.println("hi,name:"+name+";age:"+age+";address:"+address); } } package oop.day02exer; public class Student_Test { public static void main(String[] args) { Student tom=new Student("Tom",55,"sade"); tom.sayhi(); } }*/
    /*1package oop.day02exer; public class Student { String name; int age; String address; Student(String name,int age,String address){ this.name=name; this.age=age; this.address=address; } void study(){ System.out.println(name+"studing.."); } void sayhi(){ System.out.println("hi,name:"+name+";age:"+age+";address:"+address); } } package oop.day02exer; public class Student_Test { public static void main(String[] args) { Student ww=new Student("wangwu",54,"sh"); ww.sayhi(); } }*/

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70]: /images/20230528/c04f5d621ba146d3966699fe3c419c16.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 1]: /images/20230528/2558b984418f4567bd594f88eac3bc3c.png
[this.]: /images/20230528/c5773369da5940628d955f2f1a44918b.png
[20200411111040652.png]: /images/20230528/861f1df0e706436e9d07338151456dbe.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 2]: /images/20230528/9109de65a9f7402fadf5e386c396be7c.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 3]: /images/20230528/95f441a697074e39870964a6fd12eb8f.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 4]: /images/20230528/4d6e684b003f4e1389668ae68805c0e6.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70 5]: /images/20230528/c247f0a8324f4168bfff309d8383a30b.png
[20200411141056363.png]: /images/20230528/ef42391039af4aa2ac7fc720398e03e8.png