CS 596 Client-Server Programming
Java Class

1. Classes
   1. Basic Terms
   2. Fields (Class Members)
   3. Access Levels - Variables and Methods
      1. Public, Protected, Private
   4. Object Variables are References
   5. Parameter Passing - By value only
   6. Class Fields - Static
   7. Constants

class  FieldExample 
{
	public  int  sampleData = 10;

	public  void  sampleMethod() 
	{
		System.out.println( " In sample " );
	};
}

class CreateObject 
{
	public static void main( String args[] ) 
	{
		System.out.println( " Start main " );

		FieldExample  test  =  new FieldExample ( );

		test.sampleMethod();

		System.out.println(  test.sampleData  );

	}
}

• Each class compiles to its own .class file
• Execute the class with the main program

Accessible anywhere class name is accessible

Accessible in the package that contains the class

Accessible in all subclasses

Accessible in the class only

Accessible in the package that contains the class

Accessible in subclasses defined in the package that contains the class

Not accessible in subclasses defined outside the package that contains the class

class AccessLevels 
{
	public  int  publicObjectVariable ;
	protected  float  protectedObjectVariable  =  10;
	private  int[]  privateObjectVariable;

	int  noExplicitAccessLevel  =  publicObjectVariable;

	public  AccessLevels (  int  startValue  )  
	{
		System.out.println(  " Start Constructor"  );
		privateObjectVariable  =  new  int[ startValue ];
	}

	public  void  sampleMethod(  int  value  )  
	{
		System.out.println( " In method" );
		privateObjectVariable[ 1 ]  =  value;
	}
}
class TestAccessLevels 
{
	public static void main( String args[] ) 
	{
		AccessLevels	test  =  new AccessLevels ( 11 );

		test.publicObjectVariable  =  100;	// Ok
		test.protectedObjectVariable=  100;	// Ok
		test.privateObjectVariable[ 1 ]  =  100;	// Compile Error
		test.noExplicitAccessLevel  =  100;	// Ok
	}
}

class  Student  
{
	public  char  grade;
}

class PointerTest 
{

	public static void main( String args[] ) 
	{
		Student  sam  =  new  Student();

		sam.grade  =  'A';

		Student  samTwin  =  sam;

		samTwin.grade  =  'C';

		System.out.println( sam.grade );
	}
}

class  Parameter  
{
	public  void  noChangeArgument(  char  grade  )  
	{
		grade  =  'A';
	};
};

class TestParameter   
{

	public static void main( String args[] ) 
	{

		char  samGrade  =  'C';

		Parameter  Test  =  new  Parameter();

		Test.noChangeArgument(  samGrade  );

		System.out.println(  samGrade  );
	};
};

C

• Use return
• Use references (arrays or objects)

class TestParameter   
{

	public static void main( String args[] ) 
	{
		char  samGrade  =  'C';

		samGrade  =  changeGrade(  samGrade  );

		System.out.println(  samGrade  );
	};

	public  static  char  changeGrade(  char  grade  )  
	{
		switch ( grade ) 
		{
			case  'A': 
			case  'B':
				return 'A';
			case  'C':
				return 'B';
			case  'D':
			case  'F':
				return 'C';
		};
		return 'A';
	}; 
};

class TestParameter   
{

	public static void main( String args[] ) 
	{
		char[]  classGrades  =  new char[ 30 ];

		classGrades[ 1 ]  =  'B';

		TestParameter.changeArgument(  classGrades  );

		System.out.println(  classGrades[ 1 ]  );
	};

	static  public  void  changeArgument(  char[]  grade  )  
	{
		grade[1]  =  'A';
	};
};

class  Student  
{
	public  char  grade;
};

class  Parameter  
{

	public  void  changeArgument(  Student  lucky  )  
	{
		lucky.grade  =  'A';
	};
};

class TestParameter   
{

	public static void main( String args[] ) 
	{
		Student    sam  =  new Student();

		sam.grade   =  'B';

		Parameter  Test  =  new  Parameter();

		Test.changeArgument(  sam  );

		System.out.println(  sam.grade );
	};
};

Declares variables (methods) to be class variables (methods)

Same as C++ static class members

class  StaticFields  
{
	public  static  int  size  =  10;
	protected  static int[]  classArray  =  new int [ size ];

	public  int  localInt;

	static 
	{
		size  =  20;
	};

	public  static  void  classMethod(  int  value  )  
	{
		System.out.println( " In class method" );
		size  =  value;
		localInt  =  value;	// Compile Error
	}
}

class TestStaticFields  
{

	public static void main( String args[] ) 
	{
		StaticFields  	test  =  new  StaticFields  (  );
		StaticFields  	secondObject  =  new  StaticFields  (  );

		StaticFields.size  =  100;
		System.out.println(  test.size  );	// Print 100
		StaticFields.localInt  =  99;	// Compile Error
		test.localInt  =  99;
	}
}

class  Constants  
{

	public  static  final  int  SIZE  =  10;

	protected  static  final  int[] CLASS_ARRAY  =  new int [ size ];

	public  final  int  MUST_INITIALIZE_HERE;  // Compile Error

	public  final  char  grade  =  'A';
}

class TestConstants  
{

	public static void main( String args[] ) 
	{
		System.out.println(  Constants.SIZE  );	// Prints 10

		Constants  test  =  new  Constants();

		System.out.println(  test.grade   );	// Prints A

		System.out.println(  Constants.grade  );	// Compile Error
	}
}