The difference between the four access modifiers in Java and the detailed explanation of the whole process

　Client programmer: A class consumer who uses data types in his application. His goal is to collect various classes for rapid application development.

　Class creator: A programmer who creates a new data type with the goal of building a class.

　The reasons why access control exists: a. To prevent client programmers from touching parts they should not touch; b. To allow library designers to change the internal working methods of classes without worrying about affecting client programmers

java The four keywords: public, protected, default, private (they determine who can use what is defined immediately)

Scope of application

　　 Access rights Class Package Subclass Other packages

　　　　　　　∨ ∨ × × × (Package access rights, that is, available in the entire package Accessed)

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　ulate element that cannot be accessed by anyone except the type creator and the internal method of the type]

Test class)

package com.zq.demo.test1; /** * 类内 * @author Administrator */ public class Person { public String uname = "王五"; public void introduceMyself(){ System.out.println(uname); } } package com.zq.demo.test1; //同一个包 public class Student { Person p = new Person(); public void test(){ System.out.println(p.uname); } } package com.zq.demo.test1; //子类 public class Teacher extends Person{ public int age; Person p = new Person(); public void test1(){ System.out.println(p.uname); } } package com.zq.demo.test2; //不同包 import com.zq.demo.test1.Person; public class Parents { public String uname = "haha"; Person p = new Person(); public void test2(){ System.out.println(p.uname); } }

After changing the uanme in Person to protected, the class Parents reported an error The field Person .uname is not visible (indicating that it cannot be cross-packaged)

The other three have no impact

private