Lecture 2 Object Oriented Programming

1. Lecture 2Object Oriented Programming Basics of Java Language MBY

2. Agenda • Course Perspective • Interpreter VS Compiler • Programming Essentials • Value • Variable • Data Types in Java • Identifiers • Type conversions • Manipulating Variables • Reserved Words • Manipulating Values • Expression • Operator Precedence and Associatively • Primitive Vs non Primitive data types • Objects

3. Course Perspective • Learn programming in a high-level programming language. • Programming has many paradigms – Procedural – Object-Oriented – Functional – Logic • We will study Object-Oriented Programming using ‘Java’, a popular high-level object-oriented programming language.

4. Interpreter VS Compiler • An alternative to compiling your program is to interpret your program • each line of your program is translated into machine language and immediately executed • Like translating between natural languages • Compiler: human translator translates book in its entirety and then • translated book is printed and read • Interpreter: human interpreter translates each spoken statement in sequence as speaker is speaking

5. Execution of Java Program • Java uses both compilation and interpretation in a two-step process • Compiles program into byte codes – byte code is close to machine language instructions, but not quite — it is a generic “machine language” – does not correspond to any particular machine • Virtual Machine (VM) interprets byte codes into native machine language and runs it – different VM exists for different computers, since byte code does not correspond to a real machine • Same Java byte codes can be used on different computers without re-compiling source code – each VM interprets same byte codes – allows you to run Java programs by getting just byte codes from Web page • This makes Java code run cross-platform – marketing says, “Write once, run anywhere!”

6. Graphical presentation of Execution

7. Programming Essentials • Key Tools for Programming – Editors: Allows user to enter the program. Notepad, WordPad, MSWord, etc are all editors. – Compilers/Interpreters: Translates the program into target code (in machine language). – Debuggers: Allows a programmer to run the program to see the execution of the program and correct any errors. – Profilers: Used to evaluate program’s performance. – Integrated Development Environment (IDE): Combines editor, compiler, debugger and profiler or a subset into one tool. • Common Java IDEs are Eclipse, Netbeans, BlueJ, and DrJava. • We will use Netbeans IDE for the programming assignments in this course.

8. A Word of Advice • Without good command on programming any qualification in Computer Science, Computer Engineering, Information Technology and Software Engineering is “worthless”. • There is an acute shortage of programmers in the global software market and with time this shortage is increasing

9. Addressing Memory • Each location is 1 byte of memory • 1 byte = 8 bits • Each bit is an electric impulse carrying 1 or 0. • Each byte has a unique address in hexadecimal format. • CPU reads/writes data from/to memory using that address.

10. Variable • A ‘Variable’ is used to store a value inside a computer. • A variable is a space in the memory to store a value. • Three important characteristics of a variable are Type, Name and Value.

11. Type of a Variable • Among other advantages a ‘type’ binds the memory to a variable name. • The type int is of 4 bytes in Java. • Therefore, it can hold maximum of 2,147,483,647 value. • It can also hold values in negative down to -2,147,483,648.

12. Variable for Real Numbers • int cannot hold a real value. • Therefore, a type “double” is used to hold real values. • Double takes 8 bytes of memory instead of 4 bytes. • Out of the 8 bytes in a double 4 bytes are used to hold the value before the decimal point and 4 bytes for the value after the decimal point

13. Different Data Types in Java Data Type Meaning Required Memory • Byte Byte 8 bits • Short Short Integer 16 bits • Int Integer 32 bits • Long Long Integer 64 bits • Float Single Precision Floating Point 32 bits • Double Double Precision Floating Point 64 bits • Char Unicode Character 16 bits

14. Type Conversion • Java can perform conversion automatically • int value can be assigned to long. • Depends upon type compatibility • Not all type conversions implicitly allowed. • Cant assign a long value to int. • Solution – Casting

15. Type Conversion(Widening conversion) • Widening conversion is also known as upcasting. • Narrow data types are converted into broad data type with out loss of information – Both types should be compatible. e.g. Numeric types are not compatible with Boolean and char. – Destination type is larger than source type. Example • byte  int • int  long

16. Type Conversion (Narrowing Conversion) • Narrowing conversion is also known as downcasting. • Broader data type is converted into narrower data type with loss of information – Process is called casting (explicit type conversion) – Target variable = (Target-type) Source variable – int b; – float a=50.67 – b=(int)a; – Truncation??????

17. Identifier • An identifier is a series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ($) that does not begin with a digit and does not containspaces. • Some valid identifiers are Welcome1, $value, _value, m_inputField1and button7. • The name 7button is not a valid identifier, because it begins with a digit. • The name input field is not a valid identifier, because it contains a space.

18. Java Keywords abstract boolean break byte case catch char class continue default do double else extends false final finally float for if implements import instanceof int interface Long native new null package private protected public return short static super switch synchronized this throw throws transient true try void volatile while const goto

19. Operators • Mathematical Operators +, -, *, /, % Comparison Operators ==, <, >, <=, >=, != Logical Operators ||, &&, !

20. What is the Result of this Expression? • expression 6 + 2 * 3 / 6 a) 7 b) 0.5 c) 13.0 d) 4

21. Operator precedence and associativity • To evaluate an arithmetic expression two concepts needs to be understood – Operator Precedence Operator precedence controls the order in which operations are performed – Operator Associativity The associativity of an operator specifies the order in which operations of the same precedence are performed

22. Primitive data types vs. non primitive data types. • Built in data types, like int, float and char, are also called primitive data types. • Primitive data types hold only value. • Non-primitive data types are classes like String or other user defined classes. • Non-primitive data types holds both value and operations