IUPUI Computer Science: java2/OOP in Java
1. OOP concepts
Objects Classes - instances Properties Methods Events Ball demos

IUPUI Computer Science: java2/OOP in Java
2. Three Characteristics of a truly OOP environment
Inheritence Encapsulation Polymorphism

IUPUI Computer Science: java2/OOP in Java
3. Encapsulation
Starts with functions and procedures Hide data, methods when possible abstraction Make each unit stand-alone well defined interface

IUPUI Computer Science: java2/OOP in Java
4. Inheritance
Each object is subclassed from another Can have a long string of relatives Inherits properties, methods, events of all parents

IUPUI Computer Science: java2/OOP in Java
5. Polymorphism
Object can act in multiple ways Cars, Motorcycles, Chainsaws all have start methods One method, multiple parameter signatures Label myLabel = new Label(); Label myLabel = new Label("Hi there"); Label myLabel = new Label("Hi there",30);

IUPUI Computer Science: java2/OOP in Java
6. Examples: the Button classes
Show the button programs

IUPUI Computer Science: java2/OOP in Java
7. Variables in java
primitive types Object types

IUPUI Computer Science: java2/OOP in Java
8. Boolean
name boolean length 1 byte legal values true or false (no caps) default value false operations Can be used ONLY in boolean operations (=, ==, !=, !, &, &&, |, ||, ^, ?:)

IUPUI Computer Science: java2/OOP in Java
9. Boolean example
boolean continue = true; while (continue){ //code goes here... if(continue){ //code goes here... continue = false }// end if } // end while

IUPUI Computer Science: java2/OOP in Java
10. Boolean comments
booleans are NOT integers, they only take up one byte You cannot combine integer and boolean operations EG if (intVar = 10){} is NOT legal in java (thank goodness)

IUPUI Computer Science: java2/OOP in Java
11. Characters (char)
name char length 16 bit (only ONE character) legal values unicode (ASCII + extensions) default value \u0000 (null character) operations any of the typical operations assignment boolean including if , while, for, switch it can be cast into other primative types (although it might lose some information)

IUPUI Computer Science: java2/OOP in Java
12. Char Examples
char myChar = 'C' myChar = 'a'

IUPUI Computer Science: java2/OOP in Java
13. Char Notes
notice that you must refer to a char literal inside single quotes Uppercase and lowercase letters are different If you cast a char to a numeric type, the new value will reflect the unicode value of the character

IUPUI Computer Science: java2/OOP in Java
14. byte
name byte length 8 bits legal values -128 to 127 default value 0 operations Any operations, but boolean operations ALWAYS produce a boolean result

IUPUI Computer Science: java2/OOP in Java
15. int
name int length 32 bits legal values -2,147,483,648 to 2,147,483,647 default value 0 operations Any operations, but boolean operations ALWAYS produce a boolean result

IUPUI Computer Science: java2/OOP in Java
16. long
name long length 64 bits legal values -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 default value 0 operations Any operations, but boolean operations ALWAYS produce a boolean result

IUPUI Computer Science: java2/OOP in Java
17. Examples of integer types
int num1; int num2 = 3; int ans; long myLong = 3L; long myLong = (long)num2; ans = num1 + num2;

IUPUI Computer Science: java2/OOP in Java
18. Notes on integer types
You cannot always be sure what type your answer will be when you compare different types. You may need to cast an answer to be sure Remember that integer values can be positive or negative, but cannot contain decimal values

IUPUI Computer Science: java2/OOP in Java
19. More on integers
when dealing with long values, either cast explicitly to a long or use the long postfix (L) java interprets this value as an int : 5 java interprets this value as a long: 5L (note that the L is capitalized, unlike other postfixes. Lowercase 'l' looks too much like '1' (The one character)

IUPUI Computer Science: java2/OOP in Java
20. Float
name float length 4 bytes legal values @ 2 to +/- 38 default value 0.0f operations Can be used for assignment, comparison. Can be cast to other primitive types, but may lose value

IUPUI Computer Science: java2/OOP in Java
21. double
name double length 8 bytes legal values @ 2 to +/- 300 default value 0.0d operations Can be used for assignment, comparison. Can be cast to other primitive types, but may lose value

IUPUI Computer Science: java2/OOP in Java
22. Casting primitives
Conversion between primitive types The next line will cause an error!! int answer = 54.2 + 21.7; The next line will be OK int answer = (int)(54.2 + 21.7); of course, some detail will have been lost This is different than int answer = (int)54.2 + (int)21.7;

IUPUI Computer Science: java2/OOP in Java
23. postfix identifiers
used for literal values 2i, 3d, 7L Casting will work just as well, might be more clear

IUPUI Computer Science: java2/OOP in Java
24. Strings
...are OBJECTS, not primitive types!! cannot be cast cannot be compared using math operators (..at least and get the result you might expect)

IUPUI Computer Science: java2/OOP in Java
25. Wrapper objects
classes defined to encapsulate primitives start with a capital letter Float is an object, float is a primitive Wrappers exist for all primitive types

IUPUI Computer Science: java2/OOP in Java
26. Wrapper examples
float fltPrim = 3.6f; float result; Float fltClass = new Float(fltPrim); result = fltClass.toFloat();

IUPUI Computer Science: java2/OOP in Java
27. Converting primitives to String
String.valueOf(anything); Concatenation to a string will automatically call this method Wrappers also contain a toString method

IUPUI Computer Science: java2/OOP in Java
28. primitive to string examples
String myString = String.valueOf(5); Integer myInteger = new Integer(4); myString = myInteger.toString(); myString = Integer.toString(4);

IUPUI Computer Science: java2/OOP in Java
29. Strings to primitives
Most of the wrapper objects can take a String value as their initial value, and will automatically attempt to create the proper value of the appropriate type. EG Float myVal = new Float (txtInput.getText()); lblOut.setText myVal.toString();

IUPUI Computer Science: java2/OOP in Java
30. More on String to Primitive conversion
There is also a .valueOf method in the wrappers to do this: EG Float myVal = Float.valueOf (txtInput.getText()); In these cases, however, there has not been a primitive defined (!) The value has NEVER stood alone as a primitive. It has always been part of some kind of object.

IUPUI Computer Science: java2/OOP in Java
31. Warning about Wrapper objects!!!
They cannot be used in mathematical operations convert to a primitive first (floatValue(), doubleValue(), etc) first

IUPUI Computer Science: java2/OOP in Java
32. Pass by reference, pass by value
All objects are passed by reference All primitives are passed by value To pass a primitive by value, encase it in a wrapper first

• Objects
• Classes - instances
• Properties
• Methods
• Events
• Ball demos

Three Characteristics of a truly OOP environment

• Inheritence
• Encapsulation
• Polymorphism

Encapsulation

• Starts with functions and procedures
• Hide data, methods when possible
• abstraction
• Make each unit stand-alone
• well defined interface

Inheritance

• Each object is subclassed from another
• Can have a long string of relatives
• Inherits properties, methods, events of all parents

Polymorphism

• Object can act in multiple ways
• Cars, Motorcycles, Chainsaws all have start methods
• One method, multiple parameter signatures
• Label myLabel = new Label();
• Label myLabel = new Label("Hi there");
• Label myLabel = new Label("Hi there",30);

Examples: the Button classes

• Show the button programs

Variables in java

• primitive types
• Object types

Boolean

• name	boolean
  length	1 byte
  legal values	true or false (no caps)
  default value	false
  operations	Can be used ONLY in boolean operations (=, ==, !=, !, &, &&, |, ||, ^, ?:)

Boolean example

• 
  boolean continue = true;
  while (continue){
    //code goes here...
    if(continue){
       //code goes here...
      continue = false
    }// end if
  } // end while
  

Boolean comments

• booleans are NOT integers, they only take up one byte
• You cannot combine integer and boolean operations
• EG if (intVar = 10){} is NOT legal in java (thank goodness)

Characters (char)

• name	char
  length	16 bit (only ONE character)
  legal values	unicode (ASCII + extensions)
  default value	\u0000 (null character)
  operations	any of the typical operations assignment boolean including if , while, for, switch it can be cast into other primative types (although it might lose some information)

Char Examples

• char myChar = 'C'
• myChar = 'a'

Char Notes

• notice that you must refer to a char literal inside single quotes
• Uppercase and lowercase letters are different
• If you cast a char to a numeric type, the new value will reflect the unicode value of the character

byte

• name	byte
  length	8 bits
  legal values	-128 to 127
  default value	0
  operations	Any operations, but boolean operations ALWAYS produce a boolean result

int

• name	int
  length	32 bits
  legal values	-2,147,483,648 to 2,147,483,647
  default value	0
  operations	Any operations, but boolean operations ALWAYS produce a boolean result

long

• name	long
  length	64 bits
  legal values	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
  default value	0
  operations	Any operations, but boolean operations ALWAYS produce a boolean result

Examples of integer types

• int num1;
• int num2 = 3;
• int ans;
• long myLong = 3L;
• long myLong = (long)num2;
• ans = num1 + num2;

Notes on integer types

• You cannot always be sure what type your answer will be when you compare different types. You may need to cast an answer
• to be sure
• Remember that integer values can be positive or negative, but cannot contain decimal values

More on integers

• when dealing with long values, either cast explicitly to a long or use the long postfix (L)
• java interprets this value as an int : 5
• java interprets this value as a long: 5L
• (note that the L is capitalized, unlike other postfixes. Lowercase 'l' looks too much like '1' (The one character)

Float

• name	float
  length	4 bytes
  legal values	@ 2 to +/- 38
  default value	0.0f
  operations	Can be used for assignment, comparison. Can be cast to other primitive types, but may lose value

double

• name	double
  length	8 bytes
  legal values	@ 2 to +/- 300
  default value	0.0d
  operations	Can be used for assignment, comparison. Can be cast to other primitive types, but may lose value

Casting primitives

• Conversion between primitive types
• The next line will cause an error!!
• int answer = 54.2 + 21.7;
• The next line will be OK
• int answer = (int)(54.2 + 21.7);
• of course, some detail will have been lost
• This is different than
• int answer = (int)54.2 + (int)21.7;

postfix identifiers

• used for literal values
• 2i, 3d, 7L
• Casting will work just as well, might be more clear

Strings

• ...are OBJECTS, not primitive types!!
• cannot be cast
• cannot be compared using math operators
• (..at least and get the result you might expect)

Wrapper objects

• classes defined to encapsulate primitives
• start with a capital letter
• Float is an object, float is a primitive
• Wrappers exist for all primitive types

Wrapper examples

• float fltPrim = 3.6f;
• float result;
• Float fltClass = new Float(fltPrim);
• result = fltClass.toFloat();

Converting primitives to String

• String.valueOf(anything);
• Concatenation to a string will automatically call this method
• Wrappers also contain a toString method

primitive to string examples

• String myString = String.valueOf(5);
• Integer myInteger = new Integer(4);
• myString = myInteger.toString();
• myString = Integer.toString(4);

Strings to primitives

• Most of the wrapper objects can take a String value as their initial value, and will automatically attempt to create the proper
• value of the appropriate type.
• EG
• Float myVal = new Float (txtInput.getText());
• lblOut.setText myVal.toString();

More on String to Primitive conversion

• There is also a .valueOf method in the wrappers to do this:
• EG
• Float myVal = Float.valueOf (txtInput.getText());
• In these cases, however, there has not been a primitive defined (!)
• The value has NEVER stood alone as a primitive. It has always been part of some kind of object.

Warning about Wrapper objects!!!

• They cannot be used in mathematical operations
• convert to a primitive first (floatValue(), doubleValue(), etc) first

Pass by reference, pass by value

• All objects are passed by reference
• All primitives are passed by value
• To pass a primitive by value, encase it in a wrapper first