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43_[자바] 클라스 접근 제한

Class Access

Note that a class cannot be private (that would make it inaccessible to anyone but the class) or protected. So you have only two choices for class access: package access or public. If you don’t want anyone else to have access to that class, you can make all the constructors private, thereby preventing anyone but you, inside a static member of the class, from creating an object of that class. Here’s an example: 

//: access/Lunch.java
// Demonstrates class access specifiers. Make a class
// effectively private with private constructors:

class Soup1 {
  private Soup1() {}
  // (1) Allow creation via static method:
  public static Soup1 makeSoup() {
    return new Soup1();
  }
}

class Soup2 {
  private Soup2() {}
  // (2) Create a static object and return a reference
  // upon request.(The "Singleton" pattern):
  private static Soup2 ps1 = new Soup2();
  public static Soup2 access() {
    return ps1;
  }
  public void f() {}
}

// Only one public class allowed per file:
public class Lunch {
  void testPrivate() {
    // Can't do this! Private constructor:
    //! Soup1 soup = new Soup1();
  }
  void testStatic() {
    Soup1 soup = Soup1.makeSoup();
  }
  void testSingleton() {
    Soup2.access().f();
  }
} ///:~

 

 

[Thinking in Java, 160]

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