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对java中的访问限定符的理解1

可以这样理解：

“同一类中可见”------“相对于父类，在父类的{}作用域内，父类的对象可以访问全部的成员”；

“同一包中对子类可见”------“相对于父类，与父类在同一包A中，在包A里面的子类的{}作用域内，父类或者子类的对象访问父类成员的情况”；

“同一包中对非子类可见”------“相对于父类，与父类在同一包A中，在包A里面的非子类的{}作用域内，父类或者子类的对象访问父类的成员的情况”；

“不同包中对子类可见”-------“相对于父类(在包A中)，与父类不在同一包(比如包B)中，在包B里面的子类的{}作用域内，子类的对象，访问父类的成员的情况”；

“不再同一包中对非子类可见”------“相对于父类(在包A中)，与父类不在同一包(比如包B)中，在包B里面的非子类的{}作用域内，父类或者子类的对象，访问父类的成员的情况”；

下面一行一行的解释：

一、

理解：

“同一类中可见”------“相对于父类，在父类的{}作用域内，父类的对象可以访问全部的成员”；

示例：

ClassA.java

   1:  package com.test.pkg1;

2:

3:

4:

   5:  public class ClassA {

6:

   7:      public int a;

   8:      protected int b;

   9:      int c;

  10:      private int d;

11:

  12:      public void fun1(){}

  13:      protected void fun2(){}

  14:      void fun3(){}

  15:      private void fun4(){}

16:

17:

  18:      public static void main(String[] args) {

19:

  20:          ClassA classA = new ClassA();

21:

  22:          classA.a = 0;

  23:          classA.b = 0;

  24:          classA.c = 0;

  25:          classA.d = 0;

26:

  27:          classA.fun1();

  28:          classA.fun2();

  29:          classA.fun3();

  30:          classA.fun4();

31:

  32:      }

33:

34:

  35:  }

36:

编译无误！

二、

理解：

“同一包中对子类可见”------“相对于父类，与父类在同一包A中，在包A里面的子类的{}作用域内，父类或者子类的对象访问父类成员的情况”；

ClassA.java

   1:  package com.test.pkg1;

2:

3:

4:

   5:  public class ClassA {

6:

   7:      public int a;

   8:      protected int b;

   9:      int c;

  10:      private int d;

11:

  12:      public void fun1(){}

  13:      protected void fun2(){}

  14:      void fun3(){}

  15:      private void fun4(){}

16:

17:

  18:      public static void main(String[] args) {

19:

  20:          ClassA classA = new ClassA();

21:

  22:          classA.a = 0;

  23:          classA.b = 0;

  24:          classA.c = 0;

  25:          classA.d = 0;

26:

  27:          classA.fun1();

  28:          classA.fun2();

  29:          classA.fun3();

  30:          classA.fun4();

31:

  32:      }

33:

34:

  35:  }

36:

  37:  class ClassB extends ClassA{

38:

  39:      public void fun5()

  40:      {

  41:          ClassA classA = new ClassA();

  42:          ClassB classB = new ClassB();

43:

  44:          classA.a = 0;

  45:          classA.b = 0;

  46:          classA.c = 0;

  47:          classA.d = 0;

48:

  49:          classA.fun1();

  50:          classA.fun2();

  51:          classA.fun3();

  52:          classA.fun4();

53:

  54:          classB.a = 0;

  55:          classB.b = 0;

  56:          classB.c = 0;

  57:          classB.d = 0;

58:

  59:          classB.fun1();

  60:          classB.fun2();

  61:          classB.fun3();

  62:          classB.fun4();

  63:      }

  64:  }

下面是系统提示：

三、

理解：

ClassA.java

   1:  package com.test.pkg1;

2:

3:

4:

   5:  public class ClassA {

6:

   7:      public int a;

   8:      protected int b;

   9:      int c;

  10:      private int d;

11:

  12:      public void fun1(){}

  13:      protected void fun2(){}

  14:      void fun3(){}

  15:      private void fun4(){}

16:

17:

  18:      public static void main(String[] args) {

19:

  20:          ClassA classA = new ClassA();

21:

  22:          classA.a = 0;

  23:          classA.b = 0;

  24:          classA.c = 0;

  25:          classA.d = 0;

26:

  27:          classA.fun1();

  28:          classA.fun2();

  29:          classA.fun3();

  30:          classA.fun4();

31:

  32:      }

33:

34:

  35:  }

36:

  37:  class ClassB extends ClassA{}

38:

  39:  class ClassC{

40:

  41:      public void fun5()

  42:      {

  43:          ClassA classA = new ClassA();

  44:          ClassB classB = new ClassB();

45:

  46:          classA.a = 0;

  47:          classA.b = 0;

  48:          classA.c = 0;

  49:          classA.d = 0;

50:

  51:          classA.fun1();

  52:          classA.fun2();

  53:          classA.fun3();

  54:          classA.fun4();

55:

  56:          classB.a = 0;

  57:          classB.b = 0;

  58:          classB.c = 0;

  59:          classB.d = 0;

60:

  61:          classB.fun1();

  62:          classB.fun2();

  63:          classB.fun3();

  64:          classB.fun4();

  65:      }

  66:  }

下面是系统提示：

四、

理解：

ClassA.java

   1:  package com.test.pkg1;

2:

3:

4:

   5:  public class ClassA {

6:

   7:      public int a;

   8:      protected int b;

   9:      int c;

  10:      private int d;

11:

  12:      public void fun1(){}

  13:      protected void fun2(){}

  14:      void fun3(){}

  15:      private void fun4(){}

16:

17:

  18:      public static void main(String[] args) {

19:

  20:          ClassA classA = new ClassA();

21:

  22:          classA.a = 0;

  23:          classA.b = 0;

  24:          classA.c = 0;

  25:          classA.d = 0;

26:

  27:          classA.fun1();

  28:          classA.fun2();

  29:          classA.fun3();

  30:          classA.fun4();

31:

  32:      }

33:

34:

  35:  }

36:

ClassB.java

   1:  package com.test.pkg2;

2:

   3:  import com.test.pkg1.ClassA;

4:

5:

   6:  class ClassB extends ClassA{

7:

   8:      public void fun5()

   9:      {

  10:          ClassA classA = new ClassA();

  11:          ClassB classB = new ClassB();

12:

  13:          classA.a = 0;

  14:          classA.b = 0;

  15:          classA.c = 0;

  16:          classA.d = 0;

17:

  18:          classA.fun1();

  19:          classA.fun2();

  20:          classA.fun3();

  21:          classA.fun4();

22:

  23:          classB.a = 0;

  24:          classB.b = 0;

  25:          classB.c = 0;

  26:          classB.d = 0;

27:

  28:          classB.fun1();

  29:          classB.fun2();

  30:          classB.fun3();

  31:          classB.fun4();

  32:      }

  33:  }

下面是系统提示：

只需看关于ClassB的对象的提示。

五、

理解：

ClassA.java

   1:  package com.test.pkg1;

2:

3:

4:

   5:  public class ClassA {

6:

   7:      public int a;

   8:      protected int b;

   9:      int c;

  10:      private int d;

11:

  12:      public void fun1(){}

  13:      protected void fun2(){}

  14:      void fun3(){}

  15:      private void fun4(){}

16:

17:

  18:      public static void main(String[] args) {

19:

  20:          ClassA classA = new ClassA();

21:

  22:          classA.a = 0;

  23:          classA.b = 0;

  24:          classA.c = 0;

  25:          classA.d = 0;

26:

  27:          classA.fun1();

  28:          classA.fun2();

  29:          classA.fun3();

  30:          classA.fun4();

31:

  32:      }

33:

34:

  35:  }

36:

ClassB.java

   1:  package com.test.pkg2;

2:

   3:  import com.test.pkg1.ClassA;

4:

5:

   6:  class ClassB extends ClassA{

7:

8:

   9:  }

10:

11:

  12:  class ClassC{

13:

  14:      public void fun5()

  15:      {

  16:          ClassA classA = new ClassA();

  17:          ClassB classB = new ClassB();

18:

  19:          classA.a = 0;

  20:          classA.b = 0;

  21:          classA.c = 0;

  22:          classA.d = 0;

23:

  24:          classA.fun1();

  25:          classA.fun2();

  26:          classA.fun3();

  27:          classA.fun4();

28:

  29:          classB.a = 0;

  30:          classB.b = 0;

  31:          classB.c = 0;

  32:          classB.d = 0;

33:

  34:          classB.fun1();

  35:          classB.fun2();

  36:          classB.fun3();

  37:          classB.fun4();

  38:      }

  39:  }

系统提示：

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原文地址：https://www.cnblogs.com/pengdonglin137/p/2976257.html

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