JAVA学习：抽象与封装

迷南。 2022-12-18 01:56 137阅读 0赞

### 文章目录 ###

*  一、构造函数
 *   *  1、从现实中抽象出类分为三步：
     *  2、使用类图描述类
     *  3、对象初始化
 *  二、封装
 *  三、常量

# 一、构造函数 #

## 1、从现实中抽象出类分为三步： ##

1.  给具有共性特征的物体分类
2.  找出它的属性
3.  找出它的行为

## 2、使用类图描述类 ##

1.  用于分析和设计“类”
2.  直观、容易理解  
    ![在这里插入图片描述][20201024213840324.png_pic_center]

## 3、对象初始化 ##

> overload：一个类中有多个方法，同名不同参，此为overload（重载）。

在Dog.java中输入如下代码：  
如果没有名字传入的时候，小狗的名字默认为Steve。然后我们写两个函数，一个是游泳，一个是玩碟子。

public class Dog {
        
    	public String name;
    	public String color;
    	public double age;
    	public int health;
    	
    	/**默认构造函数
    	 * 特点：1.构造函数的名字与类名必须一致
    	 *       2.构造函数不能有返回值
    	 *       3.无参构造函数，为默认方法
    	*/
    	public Dog() {
        
    		name = "Steve";             //作用：设置默认值
    	}
    	
    	
    	public void swim() {
        
    		System.out.println(name + " is swimming.");
    	}
    	
    	public void playDisc() {
        
    		System.out.println(name + " is playing disc.");
    	}
    }

然后，我们在GameUi.java文件中传入两只小狗的信息：

public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog();
    		Dog d2 = new Dog();
    		
    		d1.name = "Annie";
    		d1.color = "White";
    		
    		d2.name = "Blake";
    		d2.color = "Black";
    		
    		d1.playDisc();
    		d2.swim();	
    	}
    }

点击运行，得到下面的结果：

Annie is playing disc.
    Blake is swimming.

我们也可以使用有参函数。 在同样一块作用域中，局部变量优先于成员变量。  
在Dog.java中我们写入：

public class Dog {
        
    	public String name;
    	public String color;
    	public double age;
    	public int health;
    	
    	public Dog(String name) {
        
    		this.name = name;      //this指当前对象
    		this.health = 70;      //健康值默认70
    		this.color = "Black";  //默认黑色
    	}
    	
    	
    	public void swim() {
        
    		System.out.println(name + " is swimming. ");
    	}
    	
    	public void playDisc() {
        
    		System.out.println(name + " is playing disc.");
    	}
    }

在GameUi.java中我们写入：

import com.icss.bk.biz.Dog;
    
    public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog("Annie");
    		Dog d2 = new Dog("Blake");
    		
    		d1.name = "Annie";
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		d1.playDisc();
    		System.out.println(d1.name + " is " + d1.color + ". Health status:" + " " + d1.health);
    		d2.swim();
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.health);
    	}
    
    }

运行后我们得到结果：

Annie is playing disc.
    Annie is Black. Health status: 70
    Barron is swimming. 
    Barron is Yellow. Health status: 70

我们可以尝试写多参函数：

# 二、封装 #

面向对象（OOP）：Object Orient Program  
三个重要特征：继承、封装和多态。

封装：主要作用是为了代码安全。使用关键字`private`，在作用域外不可被调用。  
现在我们给小狗加上泳姿：

public class Dog {
        
    	public String name;
    	public String color;
    	public double age;
    	public int health;
    	private String swimType;   //泳姿
    	
    	public Dog(String name) {
        
    		this.name = name;      //this指当前对象
    		this.health = 70;      //健康值默认70
    		this.color = "Black";  //默认黑色
    		this.swimType = "Doggie style";
    	}
    	public void swim() {
        
    		System.out.println(name + " is swimming, using " + this.swimType + ".");
    	}
    }

import com.icss.bk.biz.Dog;
    
    public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog("Annie");
    		Dog d2 = new Dog("Blake");
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		d2.swim();
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.health);
    	}
    
    }

得到结果：

Barron is swimming, using Doggie style.
    Barron is Yellow. Health status: 70

假如我们想在GameUi.java中调用swimTpye，是无法调用和改变的。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center]  
如果改变的话，需要回到Dog.java函数中去修改。假如我们根据水的深浅，来修改小狗的游泳姿势。  
首先，我们新建一个包，其中，entity的意思为实体包。  
**实体：只有属性，没有方法。**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 1]  
然后，我们建一个实体类，游泳池：

package com.iscc.bk.entity;
    
    public class Pool {
        
    	
    	public double length;    //游泳池长度
    	public double width;     //游泳池宽度
    	public double depth;     //游泳池高度
    	
    	public Pool(double length,double width,double depth) {
        
    		this.length = length;
    		this.width = width;
    		this.depth = depth;
    	}
    
    }

然后，我们给小狗定义一下，如果游泳池水深超过2米，则使用潜水的方式：

package com.icss.bk.biz;
    
    import com.iscc.bk.entity.Pool;
    
    public class Dog {
        
    	public String name;
    	public String color;
    	public double age;
    	public int health;
    	private String swimType;   //泳姿
    	
    	public Dog(String name) {
        
    		this.name = name;      //this指当前对象
    		this.health = 70;      //健康值默认70
    		this.color = "Black";  //默认黑色
    		this.swimType = "doggie style";
    	}
    	
    	
    	public void swim(Pool pool) {
        
    		if(pool != null) {
        
    			if(pool.depth > 2) {
        
    				this.swimType = "diving";
    			}
    			System.out.println(name + " is swimming, using " + this.swimType + ".");
    		}
    		
    	}
    	
    	public void playDisc() {
        
    		System.out.println(name + " is playing disc.");
    	}
    }

在Game.java界面，输入代码：

package com.icss.ui;
    
    import com.icss.bk.biz.Dog;
    import com.iscc.bk.entity.Pool;
    
    public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog("Annie");
    		Dog d2 = new Dog("Blake");
    		Pool pool = new Pool(100,25,3);
    		
    		d1.name = "Annie";
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		//d1.playDisc();
    		//System.out.println(d1.name + " is " + d1.color + ". Health status:" + " " + d1.health);
    		d2.swim(pool);
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.health);
    	}
    
    }

运行后，得到结果：

Barron is swimming, using diving.
    Barron is Yellow. Health status: 70

接下来，我们对健康值进行一些调整。我们可以限定，如果健康值输入为负数，或者大于100，都属于无效值。即设定范围为0道100之间。  
首先，我们将health的属性由`public`变为`private`，然后进行一次封装。鼠标右键选择Source下的Generate Getters and Setters，勾选health。![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 2]  
我们会发现，下面多了2个方法。![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 3]  
在GameUi中，我们修改部分代码内容：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 4]  
然后我们处理健康值不在0-100范围内的问题。

package com.icss.bk.biz;
    
    import com.iscc.bk.entity.Pool;
    
    public class Dog {
        
    	public String name;
    	public String color;
    	public double age;
    	private int health;
    	private String swimType;   //泳姿，私有成员
    	
    	public Dog(String name) {
        
    		this.name = name;      //this指当前对象
    		this.health = 70;      //健康值默认70
    		this.color = "Black";  //默认黑色
    		this.swimType = "doggie style";
    	}
    	
    	public int getHealth() {
        
    		if(health > 100) {
        
    			this.health = 70;   //将大于100的数调回70 
    		}
    		else if(health < 0) {
        
    			this.health = 60;    //将小于100的数调回60 
    		}
    		else {
        
    			this.health = health; //正常赋值
    		}
    		return health;
    	}
    
    	public void setHealth(int health) {
        
    		this.health = health;
    	}
    
    	public void swim(Pool pool) {
        
    		if(pool != null) {
        
    			if(pool.depth > 2) {
        
    				this.swimType = "diving";
    			}
    			System.out.println(name + " is swimming, using " + this.swimType + ".");
    		}
    		
    	}
    	
    	public void playDisc() {
        
    		System.out.println(name + " is playing disc.");
    	}
    }

然后我们把小狗的健康值调至范围以外

package com.icss.ui;
    
    import com.icss.bk.biz.Dog;
    import com.iscc.bk.entity.Pool;
    
    public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog("Annie");
    		d1.setHealth(-80);
    		
    		Dog d2 = new Dog("Blake");
    		d2.setHealth(120);
    		Pool pool = new Pool(100,25,3);
    		
    		d1.name = "Annie";
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		d1.playDisc();
    		System.out.println(d1.name + " is " + d1.color + ". Health status:" + " " + d1.getHealth());
    		d2.swim(pool);
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.getHealth());
    	}
    
    }

运行后，我们得到结果：

Annie is playing disc.
    Annie is Black. Health status: 60
    Barron is swimming, using diving.
    Barron is Yellow. Health status: 70

使用同样的方法，可以对name、color、age等进行封装。

# 三、常量 #

接下来，我们给小狗确定性别  
![在这里插入图片描述][20201026202951909.png_pic_center]  
然后，鼠标右键选择Source下的Generate Getters and Setters，勾选sex  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 5]  
接下来，为小狗赋性别  
![在这里插入图片描述][20201026203143450.png_pic_center]  
最后，我们在游泳函数中假如小狗的性别  
![在这里插入图片描述][2020102620513398.png_pic_center]  
现在，我们运行程序得到结果：

Barron: male
    Barron is swimming, using diving.
    Barron is Yellow. Health status: 70

为了避免多次输入male和female出现错误，我们可以这么操作

public class GameUi {
        
    	
    	public static final String MALE = "male";
    	public static final String FEMALE = "female";
    	
    	public static void main(String[] args) {
        
    		
    		Dog d1 = new Dog("Annie");
    		d1.setHealth(-80);
    		d1.setSex(FEMALE);
    		
    		Dog d2 = new Dog("Blake");
    		d2.setHealth(120);
    		d2.setSex(MALE);
    		Pool pool = new Pool(100,25,3);
    		
    		d1.name = "Annie";
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		d1.swim(pool);
    		System.out.println(d1.name + " is " + d1.color + ". Health status:" + " " + d1.getHealth());
    		d2.swim(pool);
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.getHealth());
    	}
    
    }

输出得到结果：

Annie: male
    Annie is swimming, using diving.
    Annie is Black. Health status: 60
    Barron: female
    Barron is swimming, using diving.
    Barron is Yellow. Health status: 70

上面的例子中，`MALE`和`FEMALE`就是常量。当然，我们还要考虑代码摆放的位置，因为放在GameUi中，在Dog中就无法调用了，因此，需要将常量封装到entity里面。我们在entity包中新建Sex类，然后将之前的两行代码从GameUi中转移至Sex中

package com.iscc.bk.entity;
    
    public class Sex {
        
    	
    	public static final String MALE = "male";
    	public static final String FEMALE = "female";
    
    }

然后在GameUi调用的时候，我们也需要将代码进行调整

public class GameUi {
        
    	
    	public static void main(String[] args) {
        
    		
    		
    		Dog d1 = new Dog("Annie");
    		d1.setHealth(-80);
    		d1.setSex(Sex.FEMALE);
    		
    		Dog d2 = new Dog("Blake");
    		d2.setHealth(120);
    		d2.setSex(Sex.FEMALE);
    		Pool pool = new Pool(100,25,3);
    		
    		d1.name = "Annie";
    		
    		d2.name = "Barron";
    		d2.color = "Yellow";
    		
    		d1.swim(pool);
    		System.out.println(d1.name + " is " + d1.color + ". Health status:" + " " + d1.getHealth());
    		d2.swim(pool);
    		System.out.println(d2.name + " is " + d2.color + ". Health status:" + " " + d2.getHealth());
    	}
    
    }

运行后，结果和之前一致。

[20201024213840324.png_pic_center]: /images/20221122/c350050988f14d18a88e693806795fec.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center]: /images/20221122/3f0b43abb57b402fb1c9aa857a022e11.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 1]: /images/20221122/1be3a4d4816b4e6ab61bfbfbb7c9aba7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 2]: /images/20221122/21a3530bfc9c4309a7485991e6b44fe4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 3]: /images/20221122/bf02ce94809e4db0965f6493cd184bf0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 4]: /images/20221122/cd81fbefbc7f4e9a91a6746057bc3826.png
[20201026202951909.png_pic_center]: /images/20221122/f4193972199b4cbe802de9148e9f8b2e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNTc0MDY5_size_16_color_FFFFFF_t_70_pic_center 5]: /images/20221122/aa82d5f12a504383afbc20507e1ac72b.png
[20201026203143450.png_pic_center]: /images/20221122/4168fdf262384f35924b0822d34b4afa.png
[2020102620513398.png_pic_center]: /images/20221122/1ec8f98d773d45bfbc9b72738c96520d.png