OnJava8_封装

• IDEA怎么设置CLASSPATH
• 一个Java源码文件被称为一个编译单元，每个编译单元的后缀必须是.java。在一个编译单元中最多有一个public类，类名必须与文件名相同。

访问权限修饰符

• public

• protected (继承可访问，包访问）

• 包访问权限
  这是默认的访问权限，通过包访问权限，使得同一包中的类可以相互访问

• private
  只能类内访问

class Sundae {
    private Sundae() {System.out.println("aaa");}
    static Sundae makeASundae() {
        return new Sundae();
    }
}

public class IceCream {
    public static void main(String[] args) {
        //- Sundae x = new Sundae();
        Sundae x = Sundae.makeASundae();
        Sundae x1 = Sundae.makeASundae();
    }
}

例子学习

class Soup1 {
    private Soup1() {}

    void count(){}

    public static Soup1 makeSoup() { // [1]
      
        return new Soup1();
    }
}

class Soup2 {
    private Soup2() {}

    private static Soup2 ps1 = new Soup2(); // [2]

    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();
    }
}