Lecture 9

Lecture Topic:

• Strings
• Vectors
• Exceptions
  
• Quiz

Strings

-- String is a character array terminated by a Null character.
 
 
 
	String WOW = "Java is great";
 
	String inst[ ] = {"you can learn", "about", "string"};
 
 
 
1. You may not change an array of character if it's used to make a string.
 
 
 
	char C_array[ ] = {'W', 'O', 'W' };
 
	String S = new String(C_array);
 
	C_array[0] = 'b';		// illegal in Java
 
 
 
2. '+' = Concatenate two or more strings.
 
   '+' = appends one string to another string.
 
 
 
	String Prog = "the professor is";
 
	String adj[ ] = {"nuts", "dumb", "boring"};
 
 
 
	String sent = Professor + adj[0];
 
	System.Out.println("String Output: " + Professor + adj[0] 
 
		+ adj[1] + adj[2]);
 
 
 

Vectors

-- vector can hold any combination of objects.

• Arrays are static, Vectors are dynamic.
• Vector does'nt hold the primitive data type such as int, char, float.

 
Syntax:
 

Vector V = new Vector();

Rectangle A = new Rectangle(10, 20);

V.addElement(A);

 
 
 
Example 1:
 
	
 
	MenuBar menuBar= new MenuBar();	// Extended from Vector
 
	SetmenuBar(menuBar);
 
	Menu Grating_menu = new Menu("Objects");	
 
	menuBar.add(Grating_menu);
 
	Grating_menu.add(new MenuItem("Grating"));
 
 
 
 
 
Example 2:
 
 
 
	ObjectMoveChoice = new Choice();	// Extended from Vector
 
	ObjectMoveChoice.addItem("Object Move");
 
	ObjectMoveChoice.addItem("Camera");
 
	add(ObjectMoveChoice);		// building a frame class
 
 
 
Example 3:
 
 
 
	public void create_geometry() {
 
		drawnShapes = new Vector();
 
		drawnShapes.addElement(grating.targetline[ ]);
 
		.....
 
	}
 
 
 
	void printObject() {
 
		Shape S;
 
		int number_of_shapes = drawnShapes.size();
 
 
 
		for (int i = 0; i <number_of_shapes; i++) {
 
 
 
		  S = (Shape)drawnShapes.elementAt(i);
 
		  S.print( );
 
		  S.move(loc);	    // move drawnShape object by Location
 
 
 
		  // store back to the same position in Vector
 
		  drawnShapes.setElementAt(S, i);	
 
		}
 
	}
 
 
 

Exceptions

-- Exceptions handle special run-time error condition.

"TRY"

execute any program statements that might throw an exception

within a "TRY" block.

"CATCH"

execute a block of code if it catch the type of exception

specified in the "CATCH" statement.

"THROW"

Toss exceptions either from your own function code or library code.

 
Syntax:
 

if () {

throw a exception() { }

}



try {

// do something that might throw an exception

}



catch (CException e) {

// handling function

//"e" contains info about the exception

}



finally {

// other handling functions

// always execute after catch, try to save the program from unexpected errors

}

 
 
 
Example 1:
 
 
 

/*-*-*-* Input Validation *-*-*-*/



Integer P1 =new Integer [2000];

Integer P2 =new Integer [3000];



Textfield P1_tf = new Textfield("Enter P1", 5);

Textfield P1_tf = new Textfield("Enter P2", 5);



Pitch_dialog.hide() {

// try to get string input

try { P1 = Integer.valueOf(P1_tf);

P2 = Integer.valueOf(P2_tf);

}



// try to catch any input format exception

catch (NumberFormatException) {

System.Out.println("****** Input Error ********");

}

}

 
 
 
Example 2:
 

if (out_of_bound) {

throw new Arithematic_Exception();

}



try {

//...What ever ...

}



catch (Arithematic_Exception e) {

System.Out.println("Out of Bound...");

}



finally {

System.Out.println("Finally I am out...");

}

Simple Quiz

 
1. String object can not be modified after it's created.
 
  a. True.
 
  b. False.
 
 
 
2. Vector class defined to model two-dimensional geometic objects.
 
  a. True.
 
  b. False.
 
 
 
3. Exceptions are always thrown with the Java "throw" statement. 
 
  a. True.
 
  b. False.