java基础 day10 继承案例多态递归

╰+攻爆jí腚メ 2023-06-06 12:29 7阅读 0赞

## 当实例化子类时（创建对象时）父类做了什么： ##

![在这里插入图片描述][2019101121234647.png]  
![在这里插入图片描述][20191011212712812.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 1]

## 继承案例: ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 2]  
代码示例：

import java.util.*;
    class Vehicle{
        
    	String brand;
    	String number;
    	public double getsumrent(int days){
        
    		return 0;
    	}
    	public Vehicle(){
        
    		
    	}
    	public Vehicle(String brand,String number){
        
    		this.brand = brand;
    		this.number = number;
    	}
    }
    class Car extends Vehicle{
        
    	String type;
    	public Car(){
        
    		System.out.println("请输入小轿车车型：");
    		Scanner input = new Scanner(System.in);
    		String c = input.next();
    		this.type = c;
    	}
    	public Car(String brand,String number,String typs){
        
    		super(brand,number);
    		this.type = type;
    	}
    	public double getsumrent(int days){
        
    		switch(this.type){
        
    		case "两厢":
    			return 300 * days;
    		case "三厢":
    			return 350 * days;
    		case "越野":
    			return 500 * days;
    		default :
    			return 0;
    		}
    	}
    }
    class Bus extends Vehicle{
        
    	int num;
    	public Bus(){
        
    		System.out.println("请输入座位数：");
    		Scanner input = new Scanner(System.in);
    		int i = input.nextInt();
    		this.num = i;
    	}
    	public Bus(String brand,String number,int num){
        
    		super(brand,number);
    		this.num = num;
    	}
    	public double getsumrent(int days){
        
    		if(this.num <= 16){
        
    			return 400 * days;
    		}
    		else {
        
    			return 600 * days;
    		}
    	}
    }
    class Test{
        
    	public static void main(String[] args){
        
    		String s1 = "小轿车";
    		String s2 = "大巴车";
    		System.out.println("请输入车型：");
    		Scanner input = new Scanner(System.in);
    		String s = input.next();
    		if(s.equals(s1)){
        
    			Car c = new Car();
    			System.out.println("请输入租用天数：");
    			Scanner ww = new Scanner(System.in);
    			int d = ww.nextInt();
    			System.out.println("租金为：" + c.getsumrent(d));
    		}
    		else if(s.equals(s2)){
        
    			Bus n = new Bus();
    			System.out.println("请输入租用天数：");
    			Scanner ee = new Scanner(System.in);
    			int x = ee.nextInt();
    			System.out.println("租金为：" + n.getsumrent(x));
    		}
    		else {
        
    			System.out.println("该车未录入");
    		}
    	}
    }

## 多态： ##

将多个对象调用同一方法，得到不同结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][20191014211803333.png]  
注意：  
当是多态时，该引用名称只能访问父类中的属性和方法，但是优先访问子类重写以后的方法。

### 例子： ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 4]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 5]  
多态好处： 减少代码的冗余性  
多态的两种类型转换：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 6]  
建议：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 7]

## 递归： ##

eg:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 8]  
内存分析：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 9]

[2019101121234647.png]: /images/20230601/5927e6dea23f4a74a9eb153a408ea4a2.png
[20191011212712812.png]: /images/20230601/94761ba89e954b2580e5350ee3417bd4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70]: /images/20230601/43372a648cb249e2bf817d1e7a91b914.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 1]: /images/20230601/1cc149b28773405299897c58428a5428.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 2]: /images/20230601/ce8617ae81a444caab0c7dc5c573ab52.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 3]: /images/20230601/5e78bf19ed044b40b5fb7848b5177fa1.png
[20191014211803333.png]: /images/20230601/e228b72f441043d3ad4d5c1910335d2b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 4]: /images/20230601/3b2b8ab522a54004939b8c39e6b8d45b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 5]: /images/20230601/4e9fb2bef4c340ba9ef74eebfc3749e7.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 7]: /images/20230601/c4b1384d333b4d89bf87ec6878162207.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxNjk0MDQ5_size_16_color_FFFFFF_t_70 9]: /images/20230601/f8008d10c74d4004a9e194c8ec7094a0.png