Java中的静止类

public class TestMyStaticClass {
     public static void main(String []args){
        MyStaticClass.setMyStaticMember(5);
        System.out.println("Static value: " + MyStaticClass.getMyStaticMember());
        System.out.println("Value squared: " + MyStaticClass.squareMyStaticMember());
        // MyStaticClass x = new MyStaticClass(); // results in compile time error
     }
}

// A top-level Java class mimicking static class behavior
public final class MyStaticClass {
    private MyStaticClass () { // private constructor
        myStaticMember = 1;
    }
    private static int myStaticMember;
    public static void setMyStaticMember(int val) {
        myStaticMember = val;
    }
    public static int getMyStaticMember() {
        return myStaticMember;
    }
    public static int squareMyStaticMember() {
        return myStaticMember * myStaticMember;
    }
}

public class Test { 
  class A { } 
  static class B { }
  public static void main(String[] args) { 
    /*will fail - compilation error, you need an instance of Test to instantiate A*/
    A a = new A(); 
    /*will compile successfully, not instance of Test is needed to instantiate B */
    B b = new B(); 
  }
}

public class A
{

 public static class B
 {
 }
}

B b = new B();

A a= new A();
B b = a.new B();

public class A {
    public static class B {

    }
}

public class C {
    A.B ab = new A.B();
}

public class C {
    A a = new A();
    A.B ab = a. new B();
}

public class OuterClass {

private static String name = "Mohammad";

// static nested class
static class StaticNestedClass {
    private int a;

    public int getA() {
        return this.a;
    }

    public String getName() {
        return name;
    }
  }
}

public class StaticNestedClassTest {

public static void main(String[] args) {

    //creating instance of static nested class
    OuterClass.StaticNestedClass nested = new OuterClass.StaticNestedClass();

    //accessing outer class static member
    System.out.println(nested.getName());    // Printing "Mohammad"
    }
}

public class MyClass {
   // Static method
   static void myStaticMethod() {
      System.out.println("Static methods can be called without creating objects");
   }

  // Public method
  public void myPublicMethod() {
      System.out.println("Public methods must be called by creating objects");
   }

  // Main method
  public static void main(String[ ] args) {
      myStaticMethod(); // Call the static method
    // myPublicMethod(); This would output an error

    MyClass myObj = new MyClass(); // Create an object of MyClass
    myObj.myPublicMethod(); // Call the public method
  }
}

public class Outer {
   static class Nested_Demo {
      public void my_method() {
          System.out.println("This is my nested class");
      }
   }
public static void main(String args[]) {
      Outer.Nested_Demo nested = new Outer.Nested_Demo();
      nested.my_method();
   }
}

/**
 * @serial include
 */
static class UnmodifiableSet extends UnmodifiableCollection
                             implements Set, Serializable {
    private static final long serialVersionUID = -9215047833775013803L;

    UnmodifiableSet(Set<? extends E> s)     {super(s);}
    public boolean equals(Object o) {return o == this || c.equals(o);}
    public int hashCode()           {return c.hashCode();}
}

public static  Set unmodifiableSet(Set<? extends T> s) {
    return new UnmodifiableSet(s);
}