Java入门学习笔记（六）——访问权限修饰符、方法的参数传递方式

Dear 丶 2022-12-10 07:25 170阅读 0赞

# 一、访问权限修饰符 #

## 1.修饰属性和方法 ##

<table> 
 <thead> 
  <tr> 
   <th></th> 
   <th>类内部</th> 
   <th>包内部</th> 
   <th>子类</th> 
   <th>包外部</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>默认</td> 
   <td>√</td> 
   <td>√</td> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>public</td> 
   <td>√</td> 
   <td>√</td> 
   <td>√</td> 
   <td>√</td> 
  </tr> 
  <tr> 
   <td>private</td> 
   <td>√</td> 
   <td></td> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>protected</td> 
   <td>√</td> 
   <td>√</td> 
   <td>√</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

## 2.修饰类 ##

<table> 
 <thead> 
  <tr> 
   <th></th> 
   <th>类内部</th> 
   <th>包内部</th> 
   <th>子类</th> 
   <th>包外部</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>默认</td> 
   <td>√</td> 
   <td>√</td> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>public</td> 
   <td>√</td> 
   <td>√</td> 
   <td>√</td> 
   <td>√</td> 
  </tr> 
  <tr> 
   <td>private</td> 
   <td>√</td> 
   <td></td> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>protected</td> 
   <td>√</td> 
   <td></td> 
   <td></td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 零碎的一些知识点 ###

1.  被private、protected修饰的类一定是内部类，对于独立定义的类，一般不能被定义为private或protected
2.  内部类只能被定义所在的类内部访问
3.  内部类不能作为超类
4.  无任何修饰的类叫做友好类
5.  在另一个类中使用友好类创建对象时，需要确保他们在同一个包内部

## 练习 ##

![在这里插入图片描述][20200924212854552.png_pic_center]

### PA ###

package PackageA;
    
    public class PA {
        
    	protected int id;
    	protected String name;
    	String sex;
    	
    	private class PA1
    	{
        
    		public void print()
    		{
        
    			System.out.println("在PA类内部定义的私有类PA1，仅供PA访问");
    		}
    	}
    	
    	protected class PA2
    	{
        
    		public void print()
    		{
        
    			System.out.println("在PA类内部定义的保护类PA2，仅供PA访问");
    		}
    	}
    	
    	public PA(int i,String s)
    	{
        
    		id=i;
    		name=s;
    	}
    	
    	protected int getId()
    	{
        
    		return id;
    	}
    	
    	String getSex()
    	{
        
    		return sex;
    	}
    	
    	public String getName()
    	{
        
    		return name;
    	}
    	
    	public void print()
    	{
        
    		System.out.println("id:"+id);
    		System.out.println("Name:"+name);
    		System.out.println("Sex:"+sex);
    	}
    	
    	public void print1()
    	{
        
    		PA1 pa1=new PA1();
    		pa1.print();
    		PA2 pa2=new PA2();
    		pa2.print();
    	}
    }

### PB ###

package PackageA;
    
    public class PB {
        
    	public static void main(String[] args)
    	{
        
    		PA a=new PA(1,"张三");
    		a.print();
    		a.id=2;
    		a.name="李四";
    		System.out.println("id:"+a.getId());
    		System.out.println("name:"+a.getName());
    	}
    }

### 运行结果 ###

![在这里插入图片描述][20200924213059345.png_pic_center]

### Test ###

package PackageB;
    
    import PackageA.*;
    
    public class TestProtected {
        
    	public static void main(String[] args)
    	{
        
    		PA a=new PA(1,"张三");
    		a.print();
    		//a.id=2;
    		//a.name="heih";
    		//System.out.println("id="+a.getId());
    		System.out.println("Name:"+a.getName());
    	}
    }

### 运行结果 ###

![在这里插入图片描述][20200924213113139.png_pic_center]

# 二、方法的参数传递方式 #

## 示例 ##

package PackageA;
    
    public class Para {
        
    	String value;
    	public static void value(String a,String b,String c,String d)
    	{
        
    		a=a.concat(b);
    		c=b;
    		d=new String(a);
    		System.out.println("改变变量值之后：a="+a+",b="+b+",c="+c+",d="+d);
    	}
    	
    	public static void change(Para a,Para b,Para c,Para d)
    	{
        
    		a.value=a.value.concat(b.value);
    		c.value=b.value;
    		d.value=new String(a.value);
    		System.out.println("改变变量值之后：a="+a+",b="+b+",c="+c+",d="+d);
    	}
    	
    	@Override
    	public String toString()
    	{
        
    		return value;
    	}
    	
    	public static void main(String[] args)
    	{
        
    		String a,b,c,d;
    		a="aaa";
    		b="bbb";
    		c="ccc";
    		d="ddd";
    		System.out.println("调用value之前：a="+a+",b="+b+",c="+c+",d="+d);
    		value(a,b,c,d);
    		System.out.println("调用value之后：a="+a+",b="+b+",c="+c+",d="+d);
    		Para a1,b1,c1,d1;
    		a1=new Para();
    		b1=new Para();
    		c1=new Para();
    		d1=new Para();
    		a1.value="aaaa";
    		b1.value="bbbb";
    		c1.value="cccc";
    		d1.value="dddd";
    		System.out.println("调用change之前：a1="+a1+",b1="+b1+",c1="+c1+",d1="+d1);
    		change(a1,b1,c1,d1);
    		System.out.println("调用change之后：a1="+a1+",b1="+b1+",c1="+c1+",d1="+d1);
    	}
    }

## 运行结果 ##

![在这里插入图片描述][20200925215803401.png_pic_center]

[20200924212854552.png_pic_center]: /images/20221123/9d47b9e6a8034b0abb440b6056801565.png
[20200924213059345.png_pic_center]: /images/20221123/412c17fb6c7948b291ab1e838e9a2979.png
[20200924213113139.png_pic_center]: /images/20221123/8403e95a95c94f79b000cf27f30ac291.png
[20200925215803401.png_pic_center]: /images/20221123/81f32751a6a549cea48c5f3f2ff96290.png